Methods and Compositions for Generating a Deletion Library and for Identifying a Defective Interfering Particle (DIP)

ABSTRACT

Provided are methods and compositions for generating a deletion library, and methods and compositions for generating and identifying a defective interfering particle (DIP). Also provided are transposon cassettes. A subject method can include: inserting a transposon cassette comprising a target sequence for a sequence specific DNA endonuclease into a population of circular target DNAs to generate a population of transposon-inserted circular target DNAs; contacting the population of transposon-inserted circular target DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear target DNAs; contacting the population of cleaved linear target DNAs with one or more exonucleases to generate a population of deletion DNAs; and circularizing the deletion DNAs to generate a library of circularized deletion DNAs. The population of circular target DNAs can include viral genomic DNA. Also provided are human immunodeficiency virus (HIV) deletion mutants, e.g., interfering, conditionally replicating, HIV deletion mutants, and related constructs.

CROSS-REFERENCE

This application is a U.S. National Stage entry of International Application No. PCT/US2017/066462, which claims the benefit of U.S. Provisional Patent Application No. 62/434,322, filed Dec. 14, 2016, the disclosures of which applications are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant Nos. 0D006677 and OD017181, awarded by the National Institutes of Health, and Grant No. D15AP00024, awarded by the Defense Advanced Research Projects Agency. The government has certain rights in the invention.

INCORPORATION BY REFERENCE OF SEQUENCE LISTING PROVIDED AS A TEXT FILE

A Sequence Listing is provided herewith as a text file, “GLAD-425WO SeqList_ST25.txt” created on Dec. 13, 2017 and having a size of 675 KB. The contents of the text file are incorporated by reference herein in their entirety.

INTRODUCTION

Circular DNAs, e.g., plasmids, have become a ubiquitous tool in molecular biology. There is a need in the art for additional methods and compositions for manipulating circular target DNAs for a variety of purposes. For example, there is a need for methods and compositions that facilitate the generation of deletion libraries (e.g., libraries of circular DNAs in which members of the library include one or more deletions at different locations relative to other members of the library).

SUMMARY

Provided are methods and compositions for generating a deletion library. In some embodiments, a subject method includes: (a) inserting a transposon cassette comprising a target sequence for a sequence specific DNA endonuclease into a population of circular target DNAs to generate a population of transposon-inserted circular target DNAs; (b) contacting the population of transposon-inserted circular target DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear target DNAs; (c) contacting the population of cleaved linear target DNAs with one or more exonucleases to generate a population of deletion DNAs; and (d) circularizing the deletion DNAs to generate a library of circularized deletion DNAs. In some cases, the transposon cassette includes a first recognition sequence positioned at or near one end of the transposon cassette and a second recognition sequence positioned at or near the other end of the transposon cassette.

In some embodiments, the circular target DNAs are plasmids that comprise a viral genome. In some such cases, the method further includes introducing members of the library of circularized deletion DNAs into mammalian cells, and assaying for viral infectivity. In some cases, the method further includes sequencing members of the library of circularized deletion DNAs to identify defective interfering particles (DIPs).

In some cases, the sequence specific DNA endonuclease is selected from: a meganuclease, a CRISPR/Cas endonuclease, a zinc finger nuclease, or a TALEN. In some cases, the one or more exonucleases includes T4 DNA polymerase. In some cases, the one or more exonucleases includes a 3′ to 5′ exonuclease and a 5′ to 3′ exonuclease. In some cases, the one or more exonucleases includes RecJ. In some cases, a subject method includes inserting a barcode sequence prior to or simultaneous with step (d). In some cases, the step of contacting the population of cleaved linear target DNAs with one or more exonucleases is performed in the presence of a single strand binding protein (SSB).

Also provided are methods of generating and identifying a defective interfering particle (DIP). In some cases, such a subject method includes (a) inserting a target sequence for a sequence specific DNA endonuclease into a population of circular target viral DNAs, each comprising a viral genome, to generate a population of sequence-inserted viral DNAs; (b) contacting the population of sequence-inserted viral DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear viral DNAs; (c) contacting the population of cleaved linear viral DNAs with an exonuclease to generate a population of deletion DNAs; (d) circularizing the deletion DNAs to generate a library of circularized deletion viral DNAs; and (e) sequencing members of the library of circularized deletion viral DNAs to identify deletion interfering particles (DIPs). In some cases, the method includes inserting a barcode sequence prior to or simultaneous with step (d).

In some cases, the method includes introducing members of the generated library of circularized deletion DNAs into cells, e.g., mammalian cells, and assaying for viral infectivity. In some cases, the inserting of step (a) includes inserting a transposon cassette into the population of circular target viral DNAs, where the transposon cassette includes the target sequence for the sequence specific DNA endonuclease, and wherein said generated population of sequence-inserted viral DNAs is a population of transposon-inserted viral DNAs. In some cases, the method includes, after step (d), infecting cells, e.g., mammalian cells in culture with members of the library of circularized deletion viral DNAs at a high multiplicity of infection (MOI), culturing the infected cells for a period of time ranging from 12 hours to 2 days, adding naive cells to the to the culture, and harvesting virus from the cells in culture. In some cases, the method includes, after step (d), infecting cells, e.g., mammalian cells in culture with members of the library of circularized deletion viral DNAs at a low multiplicity of infection (MOI), culturing the infected cells in the presence of an inhibitor of viral replication for a period of time ranging from 1 day to 6 days, infecting the cultured cells with functional virus at a high MOI, culturing the infected cells for a period of time ranging from 12 hours to 4 days, and harvesting virus from the cultured cells.

Also provided are transposon cassettes, which may be utilized, for example, in the methods described herein. In some embodiments a subject transposon cassette is a DNA molecule that includes transposase compatible inverted terminal repeats (ITRs) flanking a sequence of interest, wherein the sequence of interest includes a first copy and a second copy of a recognition sequence for a first meganuclease. In some cases the transposase compatible inverted terminal repeats (ITRs) are cable of being recognized and utilized by a Tn5 transposase. In some cases the sequence of interest includes a selectable marker gene, and the first and second copies flank the selectable marker gene. In some cases the selectable marker gene encodes an antibiotic resistance protein. In some cases the transposon cassette includes a first copy and a second copy of a recognition sequence for a second meganuclease. In some cases the first and second copies of the recognition sequence for the second meganuclease flank a selectable marker gene. In some cases the transposase compatible inverted terminal repeats (ITRs) are cable of being recognized and utilized by a Tn5 transposase.

Also provided are human immunodeficiency virus (HIV) deletion mutants, e.g., interfering, conditionally replicating, HIV deletion mutants, and related constructs identified using the screening methods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures.

FIG. 1 provides a schematic representation of one embodiment of a method of generating a deletion library. The depicted use of a barcode to tag the deletion is optional.

FIG. 2 provides a schematic representation of a circular target DNA that includes a wildtype viral genome, in this case the NL4-3 provirus of HIV-1.

FIG. 3 provides a schematic representation of two examples of transposon cassettes that can be used in the subject methods. Note: “MOD2*-Kan^(R)” is referred to as “TN5MK” in FIG. 20 and “MOD2*-Cm^(R)” is referred to as “TN5MC” in FIG. 20.

FIG. 4 provides sequence information for a portion of one example of a subject transposon cassette. The depicted stops codons, between the meganuclease recognition sequences, are an optional feature. Note: “MOD2*-Kan^(R)” is referred to as “TN5MK” in FIG. 20.

FIG. 5 depicts a plot of transposon insertion location vs genome position for transposon insertions (transposon-inserted circular target DNAs) generated using the methods disclosed herein.

FIG. 6 provides a schematic representation of molecular details of steps of one embodiment of a method of generating a deletion library.

FIG. 7 provides data from contacting a population of cleaved linear target DNAs with T4 DNA polymerase (an example of a 3′ to 5′ exonuclease) to generate a population of deletion DNAs. The exonuclease digestion of the target DNAs using T4 DNA polymerase was performed in this example in the presence or absence of RecJ (a 5′ to 3′ exonuclease) and in the presence or absence of single strand binding protein (SSB).

FIG. 8 provides the same data as FIG. 7, but the image is of a longer exposure.

FIG. 9 provides a graph showing the amount of DNA removed during exonuclease digestion as a function of time.

FIG. 10 provides a schematic representation of sequencing (e.g., deep-sequencing) members of a generated deletion library in which a barcode (e.g., barcode cassette) has been inserted.

FIG. 11 provides a histogram of deletion sizes of an HIV-1 deletion library (pNL4-3Δ₁) which was generated using methods described herein. The histogram shows a diverse range of different sized deletions. Data were obtained by deep-sequencing the deletion plasmid library.

FIG. 12 provides a plot of deletion depth vs genome location for the same library referred to in FIG. 11. The plot demonstrates that the deletion library was comprehensive (coverage over the genome) and relatively unbiased. The valley surrounding ori/bla (required for plasmid maintenance in culture) shows that bacteria harboring plasmids with deletions in this region were select against.

FIG. 13 provides a schematic representation of one method to test for infectivity of a generated deletion library where the circular target DNAs include a viral genome. For example, such a method may include a step of introducing members of the library of circularized deletion DNAs into cells, e.g., mammalian cells, and assaying for viral infectivity.

FIG. 14 provides a schematic representation of deletions that can be obtained in a generated library when the target DNA includes a viral genome.

FIG. 15 provides a representation of the type of data that can be obtained using sequencing (e.g., to identify the presence of barcodes) before and after a step of assaying for viral infectivity.

FIG. 16 provides a representation of the type of data that can be obtained using sequencing (e.g., to identify the presence of barcodes) before and after a step of assaying for viral infectivity. FIG. 17 provides a schematic representation of a “high multiplicity of infection (MOI) screen” for identifying DIPs from a generated deletion library of viral genome containing target DNAs. The indicated use of MT-4 cells is provided as an example and is not limiting.

FIG. 18 presents a plot of deletion depth vs position for the NL4-3 library after 12 high-MOI passages in a T-cell line. High deletion depth indicates that deletions are tolerated in this region, low deletion depth indicates regions intolerant of deletion. This data is used to identify regions of the genome intolerant of deletion (cis-acting elements), where trans-complementation by the wildtype virus is not possible.

FIG. 19 provides a schematic representation of a “low multiplicity of infection (MOI) screen” for identifying DIPs from a generated deletion library of viral genome containing target DNAs. The indicated use of MT-4 cells and HIV protease inhibitors is provided as an example and is not limiting.

FIG. 20 provides sequences for constructs used in the examples section. Note: “TN5MK” is referred to as “MOD2*-Kan^(R)” in FIG. 3 and FIG. 4, and “TN5MC” is referred to as “MOD2*-Cm^(R)” in FIG. 3.

FIG. 21 provides a table showing details of the pNL4-3Δ₁ deletion library of the present disclosure.

FIG. 22 provides a schematic showing the RNA genome of HIV-1. The nine protein coding genes of HIV-1 are depicted as gray rectangles, with protein domains annotated underneath each rectangle and protease cleavage sites shown as vertical dashed lines. Two of the genes are bi-exonic (tat and rev) while the remainder are mono-exonic. The LTR at the genome termini are shown as unfilled rectangles. Regions of known secondary structure and potential cis-acting elements are annotated above gene start locations and include: the 5′ untranslated region, gag-pol ribosomal frameshift, central polypurine tract/central termination sequence, Env signal-peptide stem, V1, V2, V3, V4, V5 loops of gp120; the Rev Response Element; the polypurine tract; and the 3′ UTR.

FIG. 23 provides a schematic illustrating the preparation of IIlumina sequencing libraries from PCR of barcode cassettes, version 1. Three consecutive PCR reactions were used to add adapter sequences compatible with the TruSeq sequencing system. Introduction of molecular barcodes and multiplexing barcodes, allowed for high-throughput quantification of the barcoded libraries.

FIG. 24 provides a schematic of a block design of a high-MOI passage of NL43Δ₁ according to an exemplary embodiment of the present disclosure (see also, Example 6). 293T cells were co-transfected with equal masses of pNL4-3 and pNL43Δ₁ to generate a pool of infectious virus containing both wildtype virus and deletion mutants. The common virus pool was divided and used to infect MT-4 in triplicate (K,L,M). Using a combination of cell-mediated and cell-free transfers, cell-free virus was harvested after 1 week (3 passages: K0/L0/M0), 2 weeks (6 passages (K1/L1/M1)), 3 weeks (9 passages (K2/L2/M2), and 4 weeks (12 passages (K3/L3/M3).). In addition, samples of mRNA from 293T (tx: transcription) and cell-free supernatant (enc: encapsidation) were saved. At the same time, a pool of virus containing only NL4-3 (no deletion mutants) was passaged identically (Flasks A,B,C: not shown).

FIG. 25 provides flow cytometry dot plots illustrating an example titration of HIV-1 stocks in MT-4 cells according to an exemplary embodiment of the present disclosure (see also, Example 6). 2×10⁶ MT-4 cells were infected with 100 μl of serial dilutions of an HIV-1 stock, and stained for HIV-1 Gag production (p24) at 24 hours post-infection, then assessed by flow cytometry. (DF: dilution factor, dil. MOI: MOI of dilution, est.: estimated). For each dilution, the largest flow cytometry dot plots depict side scatter (SSC) vs EGFP and the gating used to establish which cells are EGFP-positive; the small upper right plot depicts live cell gating (forward scatter (SSC) v SSC); the small lower right plot shows singlet gating (forward scatter width vs forward scatter area).

FIG. 26 provides a schematic of a HIV-1 high-MOI passage screen according to an exemplary embodiment of the present disclosure (see also, Example 6). On day 0, 2×10⁶ MT-4 (blue double discs) are infected at high MOI with a pool of virus (HIV-1) containing both wildtype (red stars) and deletion mutants (blue stars). At day 1, 10⁷ additional naive MT-4 are added and the volume expanded to 12 ml. On day 2, 6×10⁷ additional naïve MT-4 were added and the volume expanded to 72 ml. On day 3, cell-free supernatant was harvested and virus purified by ultracentrifugation.

FIG. 27 provides flow cytometry dot plots showing that high MOI is maintained throughout a week of passage for an exemplary HIV-1 high-MOI passage screen (see also, Example 6). Cells that are positive for HIV-1 capsid protein are indicated in the polygonal gate and reported as percentage of the population. For each sample, the largest flow cytometry dot plots depict side scatter (SSC) vs EGFP and the gating used to establish which cells are EGFP-positive; the small upper right plot depicts live cell gating (forward scatter (SSC) v SSC); the small lower right plot shows singlet gating (forward scatter width vs forward scatter area).

FIG. 28 provides pairwise drop plots showing R² values of 0.83-0.93 at passage 3 and passage 12, respectively, for an exemplary HIV-1 high-MOI passage screen.

FIG. 29 provides graphs showing representative mutation trajectories during high-MOI passage. Some deletions were adaptive (NL43_D01 and NL43_B04), while others were neutral (mutant 909) or deleterious (mutant 924). Data points correspond to the triplicate flasks (K,L,M) at each passage. Prevalence is in reference to the total barcode cassette pool (tagged mutants).

FIG. 30 provides a histogram showing the distribution of fitness in deletion mutants that are not extinct by passage 12 for an exemplary HIV-1 high-MOI passage screen. Of the 4390 mutants that are not extinct, 1390 (30%) are increasing in prevalence through every passage. The dashed vertical line marks the neutral fitness boundary (slope of 0).

FIG. 31 provides a graph and schematic illustrating deletion depth profile of the pNL4-3Δ₁ μlasmid deletion library for an exemplary HIV-1 high-MOI passage screen. The graph shows a peak centered on the signal peptide of env and coverage of the entire HIV-1 genome.

FIG. 32 provides a graph and schematic illustrating that the 5′ LTR and UTR are required for efficient transcription as shown for an exemplary HIV-1 high-MOI passage screen. The deletion depth profile of poly(A) RNA from transfected 293T is shown. The graph shows a region of near-zero deletion depth at the 5′ end of the genome.

FIG. 33 provides a graph and schematic illustrating that the 5′ LTR and HIV-1 RRE are required for export and encapsidation as shown for an exemplary HIV-1 high-MOI passage screen. A deletion depth profile built from tagged viral deletion mutants in the supernatant of transfected 293T. Important regions are the 5′ end of the genome (5′LTR, 5′UTR, and the RRE).

FIG. 34 provides a graph and schematic showing deletion depth profile after 3 high MOI passages in MT-4 for an exemplary HIV-1 high-MOI passage screen. Important cis-acting regions are the 5′ end of the genome (5′ LTR through Gag Matrix (p17)), cPPT/CTS, RRE, and the 3′ end of the genome (PPT-3′ LTR).

FIG. 35 provides a graph and schematic showing deletion depth profile after 6 high MOI passages in MT-4 for an exemplary HIV-1 high-MOI passage screen. Important cis-acting regions are the 5′ end of the genome (5′ LTR through Gag Matrix (p17)), cPPT/CTS, RRE, and the 3′ end of the genome (PPT-3′ LTR).

FIG. 36 provides a graph and schematic showing deletion depth profile after 12 high MOI passages in MT-4 for an exemplary HIV-1 high-MOI passage screen. Important cis-acting regions are the 5′ end of the genome (5′ LTR through Gag Matrix (p17)), cPPT/CTS, RRE, and the 3′ end of the genome (PPT-3′ LTR).

FIG. 37 provides a graph and schematic model of HIV-1 cis- and trans-acting genomic elements based on an exemplary HIV-1 high-MOI passage screen. The HIV-1 genome is composed of 4 cis-acting elements, CAE1-CAE4, and 3 trans-acting elements, TAE1-TAE3.

FIG. 38 provides a schematic of a Low MOI screen for noncytopathic HIV-1 DIPs according to an exemplary embodiment of the present disclosure. On day 0, MT-4 (blue double discs) are infected at low MOI with a pool of virus (HIV-1) containing both wildtype (red stars) and deletion mutants (blue stars). This infection occurs in the presence of an HIV-1 protease inhibitor, such as Darunavir, which restricts viral replication to a single round. Cells infected with cytopathic HIV-1 (such as the wildtype helper virus) are killed between 0 and 4 days post-infection. Uninfected cells and cells infected with deletion mutants that do not cause cell death are enriched. At 4 days post-infection, the entire population of cells is infected at high MOI with wildtype helper virus (red stars), to achieve efficient trans-complementation of deletion mutants. On day 5, the virus-containing supernatant is harvested, now enriched for deletion mutants that are non-cytopathic and retain all cis-acting elements. The virus pool can be used to infect cells at low MOI and the process iterated.

FIG. 39 provides a schematic of a block assembly strategy to generate multiply deleted strains according to an exemplary embodiment of the present disclosure. New HIV-1 mutants can be created by 7-insert Gibson Assemblies (top) or 3-insert assemblies, using previously assembled ABC and EFG blocks.

FIG. 40 provides a table showing reconstructed single contiguous deletions from pNL4-3Δ₁ according to an exemplary embodiment of the present disclosure. For each deletion, the following information are provided: block name; size of deletion in bp; location of deletion in the NL4-3 provirus genome; barcode sequence in integrated barcode cassette (top to bottom: SEQ ID NOs.: 44-55); enrichment from plasmid library to passage 12 virus in replicate K, L, and M; which genes are potentially inactivated by truncation. For example: NL43_B01 represents a 1016 bp deletion in gag and pol (bases 1636-2651 of pNL4-3/NL4-3) and was enriched 17-fold in replicate K, 21-fold in replicate L, and 19-fold in replicate M after 12 rounds of passage in MT-4.

FIG. 41 provides a graph and schematic illustrating reconstitution of adaptive single contiguous adaptive deletions of HIV-1 according to an exemplary embodiment of the present disclosure. Information is displayed in four horizontal tracks, with horizontal numbering in bp. From top to bottom: HIV-clonedDeletions mapping of adaptive HIV-1 deletions to proviral genome; HIV-genes location of HIV-1 genes; HIV-CAE Putative HIV-1-acting elements in the literature; pNL4-3, passage 12, deletion depth profile of the NL4-3Δ₁ library after twelve high MOI passages.

FIG. 42 provides a graph showing that most deletion mutants are not replication-competent (sorted by genotype) according to an exemplary embodiment of the present disclosure. MT-4 cells were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants, and evaluated for viability by PrestoBlue assay at 5 days post-infection. Each clone was assessed by two independent experiments (n=2). The shaded region represents viability (fluorescence) values within ±30% of the uninfected cell mean (naïve). The genotype of each mutant can be read off using the key and annotations in the plot. The only clones to exhibit consistent cell killing (replication) were the reconstructed wildtype (WT) and F01-only mutant (Δnef). The positive control (NL43G) exhibited expected cell-killing as well.

FIG. 43 provides a graph showing that most deletion mutants are not replication-competent (ranked by decreasing replication competence (cell killing)) according to an exemplary embodiment of the present disclosure. MT-4 cells were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants, and evaluated for viability by PrestoBlue assay at 5 days post-infection. Each clone was assessed by two independent experiments (n=2). The shaded region represents viability (fluorescence) values within ±30% of the uninfected cell mean (naïve). The only clones to exhibit consistent cell killing (replication) were the reconstructed wildtype (WT) and F01-only mutant (Δnef). The positive control (NL43G) exhibited expected cell-killing as well.

FIG. 44 provides a graph showing that select deletion mutants interfere with wildtype HIV-1 replication (24 h, -Darunavir), ordered by genotype, according to an exemplary embodiment of the present disclosure. MT-4 cells were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants and a replication competent, GFP-tagged virus (NL43G), then evaluated for wildtype infection (GFP fluorescent cells) 24 hours post infection (one round of replication). Each clone was assessed by two independent experiments (n=2): both points are plotted above in a single column. The shaded region represents GFP+ values within ±30% of the mean of the NL43G only control. Clones with values below this region interfere with wildtype viral replication, clones with values above enhance wildtype virus replication. Uninfected cells (naïve) have a background GFP+ value of ≈1%. The genotype of each mutant can be read off using the key and annotations in the plot. Replication-competent clones (annotated as WT and Δnef) did not interfere with wildtype replication.

FIG. 45 provides a graph showing that select deletion mutants interfere with wildtype HIV-1 replication (24 h, -Darunavir), ranked by decreasing ability to interfere with WT virus replication, according to an exemplary embodiment of the present disclosure. FIG. 45 provides the same data as FIG. 44 but ranked by increasing interference effect. MT-4 cells were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants and a replication competent, GFP-tagged virus (NL43G), then evaluated for wildtype infection (GFP fluorescent cells) 24 hours post infection (one round of replication). Each clone was assessed by two independent experiments (n=2): both points are plotted above in a single column. The shaded region represents GFP+ values within ±30% of the mean of the NL43G only control. Clones with values below this region interfere with wildtype viral replication, clones with values above enhance wildtype virus replication. Uninfected cells (naïve) have a background GFP+ value of ≤1%. Replication-competent clones (annotated as WT and Δnef) did not interfere with wildtype replication.

FIG. 46 provides a graph showing that select deletion mutants interfere with wildtype HIV-1 replication (24 h, -Darunavir), ordered by genotype, according to an exemplary embodiment of the present disclosure. MT-4 cells were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants and a replication competent, GFP-tagged virus (NL43G), then evaluated for wildtype infection (GFP fluorescent cells) 24 hours post infection (one round of replication). MT-4 cells were cultured in the presence of 500 nM Darunavir, an HIV-1 protease inhibitor, to restrict subsequent transmission post-infection. Each clone was assessed by two independent experiments (n=2): both points are plotted above in a single column. The shaded region represents GFP+ values within ±30% of the mean of the NL43G only control. Clones with values below this region interfere with wildtype viral replication, clones with values above enhance wildtype virus replication. Uninfected cells (naïve) have a background GFP+ value of ≤1%. The genotype of each mutant can be read off using the key and annotations in the plot. Replication-competent clones (annotated as WT and Δnef) did not interfere with wildtype replication.

FIG. 47 provides a graph showing that select deletion mutants interfere with wildtype HIV-1 replication (48 h, -Darunavir), ordered by genotype, according to an exemplary embodiment of the present disclosure. MT-4 were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants and a replication competent, GFP-tagged virus (NL43G), then evaluated for wildtype infection (GFP fluorescent cells) 24 hours post infection (one round of replication). Each clone was assessed by two independent experiments (n=2): both points are plotted above in a single column. The shaded region represents GFP+ values within ±30% of the mean of the NL43G only control. Clones with values below this region interfere with wildtype viral replication, clones with values above enhance wildtype virus replication. Uninfected cells (naïve) have a background GFP+ value of ≤1%. The genotype of each mutant can be read off using the key and annotations in the plot. Replication-competent clones (annotated as WT and Δnef) did not interfere with wildtype replication.

FIG. 48 provides a graph showing that select deletion mutants interfere with wildtype HIV-1 replication (48 h, -Darunavir), ranked by decreasing ability to interfere with WT virus replication, according to an exemplary embodiment of the present disclosure. FIG. 48 provides the same data as FIG. 47 but ranked by increasing interference effect. MT-4 cells were infected with viral inocula produced by transfection of 293T with cloned HIV-1 mutants and a replication competent, GFP-tagged virus (NL43G), then evaluated for wildtype infection (GFP fluorescent cells) 24 hours post infection (one round of replication). Each clone was assessed by two independent experiments (n=2): both points are plotted above in a single column. The shaded region represents GFP+ values within ±30% of the mean of the NL43G only control. Clones with values below this region interfere with wildtype viral replication, clones with values above enhance wildtype virus replication. Uninfected cells (naïve) have a background GFP+ value of ≤1%. Replication-competent clones (annotated as WT and Δnef) did not interfere with wildtype replication.

FIG. 49 provides gel images indicating that deletion mutants can be mobilized by providing missing common goods in trans according to an exemplary embodiment of the present disclosure. Deletion mutant pseudovirus stocks were prepared by packaging HIV-1 mutants in 293T by co-transfection with a VSV-G envelope plasmid and pCMVRΔ8.91, which provides four HIV-1 proteins (Gag, Pol, Tat, Rev). After 5 days of recovery in the presence of 500 nM Darunavir (an HIV-1 protease inhibitor), PCR for blocks B and D was performed on DNA isolated from the transduced cells. Each pair of lanes is marked with the BTN strain number in Table 5 (e.g. 427 is BTN427, 405 is BTN405), where B corresponds to the block B amplicon and D to the block D amplicon. The wildtype (undeleted) block B amplicon is 1.9 kbp and the WT block D amplicon is 1.5 kbp. A distinct, heavy band at size less than the WT amplicon indicates that the deletion mutant had been successfully mobilized and did not kill transduced cells. Control abbreviations are WT (infected with NL43G only), mk (mock-transfection, no deletion mutant genome was added to transfection), NTC (no template control, PCR with water as template).

FIG. 50 shows Table 9, which serves as map between the data in FIGS. 43, 45, 48 and the sequence associated with each pair of 76 datapoints.

DETAILED DESCRIPTION

As summarized above, methods and compositions for generating a deletion library, and methods and compositions for generating and identifying a defective interfering particle (DIP) are provided. Also provided are transposon cassettes, which may be utilized, for example, in the methods described herein. In addition, the present disclosure provides human immunodeficiency virus (HIV) deletion mutants, e.g., interfering, conditionally replicating, HIV deletion mutants, and related constructs identified using the screening methods described herein.

Before the present methods and compositions are described, it is to be understood that this invention is not limited to the particular methods or compositions described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, some potential and preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. It is understood that the present disclosure supersedes any disclosure of an incorporated publication to the extent there is a contradiction. The complete disclosure of U.S. Patent Application Publication No. 2016-0015759 is incorporated by reference herein.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a cell” includes a plurality of such cells and reference to “the endonuclease” includes reference to one or more endonucleases and equivalents thereof, known to those skilled in the art, and so forth. It is further noted that the claims may be drafted to exclude any element, e.g., any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

Methods and Compositions

Provided are methods of generating a deletion library. Generally, members of a circular target DNA population are cleaved at different positions relative to one another to generate a library of cleaved (linearized) target DNAs where members of the library are cut at different locations. One or more exonucleases are then used to ‘chew back’ the end(s) of the cut site and the ‘chewed ends’ are then ligated to reform circular DNA. This generates a deletion library. There are numerous ways to achieve each of the steps (e.g., the cleavage step at different positions for the members of the library), and there are optional steps that can be performed prior to the circularizing (e.g., ligation) step. As discussed in more detail below, more than one round of library generation can be performed, and thus the subject methods can be used the generate complex deletion libraries in which members of the library include more than one deletion.

Generating a Library of Cleaved (Linearized) Target DNAs

Provided are methods that include generating a library of cleaved (linearized) target DNAs from a population of circular target DNAs. In some cases, the position of cleavage of the target DNA population is random. For example, a transposon cassette can be inserted at random positions into a population of target DNAs, where the transposon cassette includes a target sequence (recognition sequence) for a sequence specific DNA endonuclease. In such a case, the transposon cassette is being used as a vehicle for inserting a recognition sequence into the population of target DNAs (at random positions). A sequence specific DNA endonuclease (one that recognizes the recognition sequence) can then be used to cleave the target DNAs, thereby generating a library of cleaved (linearized) target DNAs where members of the library are cut at different locations.

The term “transposon cassette” is used herein to mean a nucleic acid molecule that includes a ‘sequence of interest’ flanked by sequences that can be used by a transposon to insert the sequence of interest into a target DNA. Thus, in some cases, the ‘sequence of interest’ is flanked by transposon compatible inverted terminal repeats (ITRs), i.e., ITRs that are recognized and utilized by a transposon. In cases where a transposon cassette is used as a vehicle for inserting one or more target sequences (for one or more sequence specific DNA endonucleases) into target DNAs, the sequence of interest can include the one or more recognition sequences.

In some cases, the sequence of interest includes a selectable marker gene, e.g., a nucleotide sequence encoding a selectable marker such as a gene encoding a protein that provides for drug resistance, e.g., antibiotic resistance. In some cases, a sequence of interest includes a first copy and a second copy of a recognition sequence for a first sequence specific DNA endonuclease (e.g., a first meganuclease). In some cases, a sequence of interest includes a selectable marker gene flanked by a first and second recognition sequence for a sequence specific DNA endonuclease (e.g., meganuclease). In some such cases, the first recognition sequence and the second recognition sequence are identical, and can be considered a first copy and a second copy of a recognition sequence. In some such cases, the first recognition sequence is different than the second recognition sequence. In some cases, the first recognition sequence and second recognition sequence (e.g., first and second copies of a recognition sequence) flank a selectable marker gene, e.g., one that encodes a drug resistance protein such as an antibiotic resistance protein. In some embodiments, a subject transposon cassette includes a first copy and a second copy of a recognition sequence for a first meganuclease; and a first copy and a second copy of a recognition sequence for a second meganuclease. In any of the above scenarios, in some cases, the first and/or second recognition sequence is a site for I-Scel (e.g., aactataacggtcctaa{circumflex over ( )}ggtagcgaa (SEQ ID NO: 1)). in some cases, the first and/or second recognition sequence is a site for I-Ceul (e.g., aactataacggtcctaa{circumflex over ( )}ggtagcgaa (SEQ ID NO: 2)). In some cases, a first recognition sequence is a site for I-Scel and a second recognition sequence is a site for I-Ceul. In some cases a first and/or second recognition sequence is a recognition sequence for a meganuclease, e.g., selected from: a LAGLIDADG meganuclease (LMNs), I-Scel, I-Ceul, I-Crel, I-Dmol, I-Chul, I-Dirl, I-Flmul, I-Flmull, I-Anil, I-ScelV, I-Csml, I-PanI, I-PanII, I-PanMI, I-Scell, I-Ppol, l-SceIII, I-LtrI, I-GpiI, I-GZeI, I-Onul, I-HjeMI, I-Msol, I-TevI, I-TevII, I-TevIII, PI-MIel, PI-Mtul, PI-Pspl, PI-Tli I, PI-Tli II, and PI-SceV.

As noted above, a subject transposon cassette includes a sequence of interest flanked by transposase compatible inverted terminal repeats (ITRs). The ITRs can be compatible with any desired transposase, e.g., a bacterial transposase such as Tn3, Tn5, Tn7, Tn9, Tn10, Tn903, Tn1681, and the like; and eukaryotic transposases such as Tc1/mariner super family transposases, piggyBac superfamily transposases, hAT superfamily transposases, Sleeping Beauty, Frog Prince, Minos, Himarl, and the like. In some cases, the transposase compatible ITRs are compatible with (i.e., can be recognized and utilized by) a Tn5 transposase. Some of the methods provided in this disclosure include a step of inserting a transposase cassette into a target DNA. Such a step includes contacting the target DNA and the transposon cassette with a transposase. In some cases this contacting occurs inside of a cell such as a bacterial cell, and in some cases this contacting occurs in vitro outside of a cell. As the transposase compatible

ITRs listed above are suitable for compositions and methods disclosed herein, so too are the transposases. As such, suitable transposases include but are not limited to bacterial transposases such as Tn3, Tn5, Tn7, Tn9, Tn10, Tn903, Tn1681, and the like; and eukaryotic transposases such as Tc1/mariner super family transposases, piggyBac superfamily transposases, hAT superfamily transposases, Sleeping Beauty, Frog Prince, Minos, Himar1, and the like. In some cases, the transposase is a Tn5 transposase.

In some embodiments, a subject method includes a step of inserting a target sequence (e.g., one or more target sequences) for a sequence specific DNA endonuclease (e.g., one or more sequence specific DNA endonucleases) into a population of circular target DNAs, thereby generating a population of sequence-inserted circular target DNAs. In some cases, the inserting step is carried out by inserting a transposon cassette that includes the target sequence (e.g., the one or more target sequences), thereby generating a population of transposon-inserted circular target DNAs. In some cases, the transposon cassette includes a single recognition sequence (e.g., in the middle or near one end of the transposon cassette) and can therefore be used to introduce a single recognition sequence into the population of target DNAs. In some cases, the transposon cassette includes more than one recognition sequences (e.g., a first and a second recognition sequence). In some such cases, the first and second recognition sequences are positioned at or near the ends of the transposon cassette (e.g., within 20 bases, 30 bases, 50 bases, 60 bases, 75 bases, or 100 bases of the end) such that cleavage of the first and second recognition sequences effectively removes the transposon cassette (or most of the transposon cassette) from the target DNA, while simultaneously generating a linearized target DNA, and therefore generating the desired library of cleaved (linearized) target DNAs where members of the library are cut at different locations.

In some cases when the transposon cassette include first and second recognition sequences, the first and second recognition sequences are the same, and are therefore first and second copies of a given recognition sequence. In some such cases, the same sequence specific DNA endonuclease (e.g., restriction enzyme, meganuclease, programmable genome editing nuclease) can then be used to cleave at both sites.

In some embodiments, the transposon cassette includes a first and a second recognition sequence where the first and second recognition sequences are not the same. In some such cases, a different sequence specific DNA endonuclease (e.g., restriction enzyme, meganuclease, programmable genome editing nuclease) is used to cleave the two sites (e.g., the library of transposon-inserted target DNAs can be contacted with two sequence specific DNA endonucleases). However, in some cases one sequence specific DNA endonuclease can still be used. For example, in some cases two different guide RNAs can be used with the same CRISPR/Cas protein. As another example, in some cases a given sequence specific DNA endonuclease can recognize both recognition sequences.

In some cases, the population of circular target DNAs (e.g., plasmids) are present inside of host cells (e.g., bacterial host cells such as E. coli) and the step of inserting a transposon cassette takes place inside of the host cell (e.g., by introducing a transposase and/or a nucleic acid encoding a transposase into the cell; by inducing expression of a transposase, e.g., where the host cell already includes a nucleic acid encoding the transposase; and the like). In some such cases, a subject method can include a selection/growth step in the host cell. For example, if the transposon cassette includes a drug resistance marker, the host cells can be grown in the presence of drug to select for those cells harboring a transposon-inserted circular target DNA.

Once a population of transposon-inserted circular target DNAs is generated (and in some cases after a selection/growth step in the host cells), they can be isolated/purified from the host cells prior to the next step (e.g., prior to contacting them with a sequence specific DNA endonuclease).

In some cases (e.g., when the circular target DNAs are small circular DNAs, e.g., less than 50 kb), a selection and growth step in bacteria can be avoided through the use of in vitro rolling circle amplification (RCA). For example, after repair of nicked target DNA post-transposition, a highly-processive and strand-displacing polymerase (e.g., phi29 DNA polymerase), along with primers specific to the inserted transposon cassette, can be used to selectively amplify insertion mutants from the pool of circular plasmids. In other words, such a step can circumvent amplifying DNA through bacterial transformation. Use of RCA can decrease the time required for growth/selection of bacteria and can avoid biasing the library towards clones that do not impede bacterial growth.

Non-Random Cleavage

As noted above, in some cases the position of cleavage of the target DNA population is random, however in some cases the position of cleavage is not random. For example, a population of target DNAs can be distributed (e.g., aliquoted) into different vessels (e.g., different tubes, different wells of a multi-well plate etc.). If a sequence of interest is known (e.g., a viral genome sequence), that is present in the population of target DNAs, then target DNAs in vessels (e.g., wells of the multi-well plate) can be cleaved at different pre-determined locations by using a programmable sequence specific endonuclease. For example, if a CRISPR/Cas endonuclease (e.g., Cas9, Cpf1, and the like) is used, guide RNAs can readily be designed to target any desired sequence within the target population (e.g., while taking protospacer adjacent motif (PAM) sequence requirements into account in some cases). For example, guide RNAs can be tiled at any desired spacing (e.g., every 5 nucleotides (nt), every 10 nt, every 20 nt, every 50nt—overlapping, non-overlapping, and the like) along a sequence of interest, and the target DNAs in each vessel (e.g., each well) can be contacted with one of the guide RNAs in addition to the CRISPR/Cas endonuclease. In this way, a library of cleaved target DNAs can be generated where members of the library are separated from one another because they are in separate vessels. As would be understood by one of ordinary skill in the art, in some cases, one would take PAM sequences into account when designing guide RNAs, and therefore the spacing between guide RNA target sites can be a function of PAM sequence constraints, and consistent spacing across a given target sequence would not necessarily be possible in some cases. However, different CRISPR/Cas endonucleases (e.g., even the same protein, such as Cas9, isolated from different species) can have different PAM requirements, and thus, the use of more than one CRISPR/Cas endonuclease can in some cases relieve at least some of the constraints imposed by PAM requirements on available target sites.

The remaining steps can then be carried out separately (e.g., in separate vessels, in separate wells of a multi-well plate), or at any step, members can be pooled and treated together in one vessel. As an illustrative but non-limiting example, one could use 96 different guide RNAs (or 384 different guide RNAs) to cleave target DNAs in 96 different wells of a 96-well plate (or 384 different wells of a 384 well plate), to generate 96 members (or 384 members) of a library where each member is cleaved at a different site (and in this case the sites are designed by the user prior to starting the method). The exonuclease step (chew back) can then be performed in separate wells (e.g., by aliquoting exonuclease to each well), or wells can be pooled prior to adding exonuclease to the pool.

Circular Target DNAs

A circular target DNA of a population of circular target DNAs can be any circular target DNA. In some cases, the circular target DNAs are plasmid DNAs, e.g., in some cases, the circular target DNAs include an origin of replication (ORI). In some cases, the circular target DNAs include a drug resistance marker (e.g., a nucleotide sequence encoding a protein that provides for drug resistance). In some embodiments, a population of circular target DNAs are generated from a population of linear DNA molecules (e.g., via intramolecular ligation). For example, a subject method can include a step of circularizing a population of linear DNA molecules (e.g., a population of PCR products, a population of linear viral genomes, a population of products from a restriction digest, etc.) to generate a population of circular target DNAs. In some cases, members of such a population are identical (e.g., many copies of a PCR product or restriction digest can be used to generate a population of circular DNAs, where each circular DNA is identical). In some cases, members of such a population can be different from one another (e.g., two or more different PCR products or restriction digest products can be circularized).

In some embodiments, the members of a population of circular target DNAs are identical (are copies of one another). In some embodiments, the members of a population of circular target DNAs are not identical (e.g., in some cases the population of circular target DNAs can itself be a deletion library). For example, the population of circular target DNAs can be a library of known deletion mutants (e.g., known viral deletion mutants). As another example, if two rounds of a subject method are performed, the starting population of target DNAs for the second round can be a deletion library (e.g., generated during a first round of deletion) where members of the library include deletions of different sections of DNA relative to other members of the library. Such a library can serve as a population of circular target DNAs, e.g., a transposon cassette can still be introduced into the population. Performing a second round of deletion in this manner can therefore generate constructs with deletions at multiple different entry points. As an illustrative example, for a target DNA of 20 kb (kilobases) in length, the first round of deletion might have deleted bases 2000 through 2650 for a one member (of the library that was generated), of which multiple copies would likely be present. A second round of deletion might generate two new members, both of which are generated from copies of the same deletion member. Thus, for example, one new member might be generated with bases 3500 through 3650 deleted (in addition to bases 2000 through 2650), while a second new member might be generated with bases 1500 through 1580 deleted (in addition to bases 2000 through 2650). Thus, multiple rounds of deletion (e.g., 2, 3, 4, 5, etc.) can produce complex deletion libraries. In some cases, more than one round of library generation is performed where the second round includes the insertion of a transposon cassette, e.g., as described above.

For example, in some cases, a first round of deletion is performed using a CRISPR/Cas endonuclease to generate the cleaved linear target DNAs by targeting the CRISPR/Cas endonuclease to pre-selected sites within the population of circular target DNAs (e.g., by designing guide RNAs, e.g., at pre-selected spacing, to target a known sequence of interest such as a viral genome). After exonuclease treatment and circularization to generate a first library of circularized deletion DNAs, the library of circularized deletion DNAs is used as input (a population of circular target DNAs) for a second round of deletion. Thus, one or more target sequences for one or more sequence specific DNA endonucleases (e.g., one or more meganucleases) is inserted (e.g., at random positions via a transposon cassette) into the library of circularized deletion DNAs to generate a population of transposon-inserted circular target DNAs, and the method is continued. In some such cases, the first round of deletion might only target a small number of locations of interest for deletion (one location, e.g., using only one guide RNA that targets a particular location; or a small number of locations, e.g., using a small number of guide RNAs to target a small number of locations), while the second round is used to generate deletion constructs that include the first deletion plus a second deletion.

Viral Genome

In some cases, the circular target DNAs include a viral genome (e.g., a whole viral genome, a viral genome that includes a deletion, a partial viral genome, etc.). Thus, in some cases the subject methods are used to generate a library of viral deletion mutants. In some such cases, a library of generated viral deletion mutants can be considered a library of potential defective interfering particles (DIPs). DIPs are mutant versions of viruses that include genomic deletions such that they are unable to replicate except when complemented by wild-type virus replicating within the same cell. DIPs can arise naturally because viral genomes encode both cis- and trans-acting elements. Trans-acting elements (trans-elements) code for gene products, such as capsid proteins or transcription factors, and cis-acting elements (cis-elements) are regions of the viral genome that interact with trans-element products to achieve productive viral replication including viral genome amplification, encapsidation, and viral egress. In other words, the viral genome of a DIP can still be copied and packaged into viral particles if the missing (deleted) trans-elements are provided in trans (e.g., by a co-infecting virus). In some cases, a DIP can be used therapeutically to reduce viral infectivity of a co-infecting virus, e.g., by competing for and therefore diluting out the available trans-elements. In some cases, a DIP can be used as a therapeutic (e.g., as a treatment for viral disease), and in some cases a DIP is therefore referred to as a therapeutic interfering particle (TIP). While DIPs can arise naturally, methods of this disclosure can be used to generate DIPs, e.g., by generating a deletion library of viral genomes. DIPs can then be identified from such a deletion library by sequencing the library members to identify those predicted to be DIPs. Alternatively, or in addition, a generated deletion library can be screened, e.g., by introducing the library into cells, to identify those members with viral genomes having the desired function. Additional description of DIPs and TIPs and uses thereof is provided in U.S. Patent Application Publication No. 20160015759, the disclosure of which is incorporated by reference herein in its entirety.

Thus, in some cases a subject method includes introducing members of the library of generated deletion constructs (e.g., deletion-containing viral genomes) into a target cell (e.g., a eukaryotic cell, such as a mammalian cell, such as a human cell) and assaying for infectivity. In some such cases, the assaying step also includes complementation of the library members with a co-infecting virus.

Such introducing is meant herein to encompass any form of introduction of nucleic acids into cells (e.g., electroporation, transfection, lipofection, nanoparticle delivery, viral delivery, and the like). For example, such ‘introduction’ encompasses infecting mammalian cells in culture (e.g., with members of a generated library of circularized deletion viral DNAs, i.e., with viral particles that contain viral genomes encoded by the members of the generated library of circularized deletion viral DNAs). In some cases, as described in more detail below, a method includes generating from the generated library of circularized deletion DNAs, at least one of: linear double stranded DNA (dsDNA) products, linear single stranded DNA (ssDNA) products, linear single stranded RNA (ssRNA) products, and linear double stranded RNA (dsRNA) products. Thus in some such cases, a subject method includes introducing said linear dsDNA products, linear ssDNA products, linear ssRNA products, and/or linear dsRNA products into mammalian cells (e.g., via any convenient method for introducing nucleic acids into cells, including but not limited to electroporation, transfection, lipofection, nanoparticle delivery, viral delivery, and the like). Such methods can also include assaying for viral infectivity.

Assaying for viral infectivity can be performed using any convenient method and many various methods will be known to one of ordinary skill in the art. Assaying for viral infectivity can be performed on the cells into which the members of the library of circularized deletion DNAs (and/or at least one of: linear double stranded DNA (dsDNA) products, linear single stranded

DNA (ssDNA) products, linear single stranded RNA (ssRNA) products, and linear double stranded RNA (dsRNA) products generated from the library of circularized deletion DNAs) are introduced. For example, in some cases the members and/or products are introduced via virus.ln some cases, members of the library of circularized deletion DNAs (and/or at least one of: linear dsDNA products, linear ssDNA products, linear ssRNA products, and linear dsRNA products generated from the library of circularized deletion DNAs) are introduced into a first population of cells (e.g., mammalian cells) in order to generate viral particles, and the viral particles are then used to contact a second population of cells (e.g., mammalian cells). Thus, as used herein, unless otherwise explicitly described, the phrase “assaying for viral infectivity” encompasses both of the above scenarios (e.g., encompasses assaying for infectivity in the cells into which the members and/or products were introduced, and also encompasses assaying the second population of cells as described above).

In some embodiments a subject method (e.g., a method of generating and identifying a DIP) includes, after generating a deletion library (e.g., a library of circularized deletion viral DNAs), a high multiplicity of infection (MOI) screen (e.g., utilizing an MOI of ≥2). As used herein, a “high MOI” is an MOI of 2 or more (e.g., 2.5 or more, 3 or more, 5 or more, etc.). In some cases, a subject method uses a high MOI. Thus, in some cases, a subject method uses an MOI (a high MOI) of 2 or more, 3 or more, or 5 or more. In some cases, a subject method uses an MOI (a high MOI) in a range of from 2-150 (e.g., from 2-100, 2-80, 2-50, 2-30, 3-150, 3-100, 3-80, 3-50, 3-30, 5-150, 5-100, 5-80, 5-50, or 5-30). In some cases, a subject method uses an MOI (a high MOI) in a range of from 3-100 (e.g., 5-100). At high MOI, many (if not all) cells are infected by more than one virus, which allows for complementation of defective viruses by wildtype counterparts. Repeated passaging of deletion mutant libraries at high-MOI can select for mutants that can be mobilized effectively by a wild type virus (e.g., HIV-1) (e.g., FIG. 17). For example, in some cases the method includes infecting mammalian cells in culture with members of the library of circularized deletion viral DNAs at a high multiplicity of infection (MOI), culturing the infected cells for a period of time ranging from 12 hours to 2 days (e.g., from 12 hours to 36 hours or 12 hours to 24 hours), adding naive cells to the to the culture, and harvesting virus from the cells in culture. However, this screening step can in some cases select for DIPs/TIPs which can be mobilized effectively by the wildtype virus, but are cytopathic in the absence of the wildtype coinfection.

Thus, in some embodiments a subject method (e.g., a method of generating and identifying a DIP) includes a more stringent screen (referred to herein as a “low multiplicity of infection (MOI) screen”). As used herein, a “low MOI” is an MOI of less than 1 (e.g., less than 0.8, less than 0.6, etc.). In some cases, a subject method uses a low MOI. Thus, in some cases, a subject method uses an MOI (a low MOI) of less than 1 (e.g., less than 0.8, less than 0.6). In some cases, a subject method uses an MOI (a low MOI) in a range of from 0.001-0.8 (e.g., from 0.001-0.6, 0.001-0.5, 0.005-0.8, 0.005-0.6, 0.01-0.8, or 0.01-0.5). In some cases, a subject method uses an MOI (a low MOI) in a range of from 0.01-0.5. For example, a low-MOI infection of target cells with a deletion library (e.g., utilizing an MOI of <1) can be alternated with a high-MOI infection of the transduced population with wildtype virus (e.g., HIV-1) to mobilize

DIPs to naive cells (e.g., see FIG. 19). In between successive infections, the cells can be propagated in the presence of a drug to prevent further rounds of replication (e.g., using a protease inhibitor such as Darunavir for HIV-1). During the recovery period, cells infected with wild type virus (e.g., HIV-1 infected cells) will be killed, but cells transduced by well-behaving mutants (which do not produce cell-killing trans-factors) will be maintained. In this fashion, mutants that do not kill their transduced host-cell but can mobilized during wildtype virus coinfection can be selected. Thus, in some cases a subject method includes infecting mammalian cells in culture with members of the library of circularized deletion viral DNAs at a low multiplicity of infection (MOI), culturing the infected cells in the presence of an inhibitor of viral replication for a period of time ranging from 1 day to 6 days (e.g., from 1 day to 5 days, from 1 day to 4 days, from 1 day to 3 days, or from 1 day to 2 days), infecting the cultured cells with functional virus at a high MOI, culturing the infected cells for a period of time ranging from 12 hours to 4 days (e.g., 12 hours to 72 hours, 12 hours to 48 hours, or 12 hours to 24 hours), and harvesting virus from the cultured cells.

In some embodiments, a subject method includes (a) inserting a target sequence for a sequence specific DNA endonuclease into a population of circular target viral DNAs, each comprising a viral genome, to generate a population of sequence-inserted viral DNAs; (b) contacting the population of sequence-inserted viral DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear viral DNAs; (c) contacting the population of cleaved linear viral DNAs with an exonuclease to generate a population of deletion DNAs; (d) circularizing (e.g., via ligation) the deletion DNAs to generate a library of circularized deletion viral DNAs; and (e) sequencing members of the library of circularized deletion viral DNAs to identify deletion interfering particles (DIPs). In some cases, the method includes inserting a barcode sequence prior to or simultaneous with step (d).

In some cases the inserting of step (a) includes inserting a transposon cassette into the population of circular target viral DNAs, wherein the transposon cassette includes the target sequence for the sequence specific DNA endonuclease, and where the generated population of sequence-inserted viral DNAs is a population of transposon-inserted viral DNAs. In some cases (e.g., in some cases when using a CRISPR/Cas endonuclease—as discussed above), a subject method does not include step (a), and the first step of the method is instead cleaving members of the library in different locations relative to one another, which step can be followed by the exonuclease step.

Target Sequence and Sequence Specific DNA Endonucleases

In some cases a target sequence for a sequence specific DNA endonuclease is inserted into a target DNA, e.g., population of target DNAs, e.g., in some cases via insertion of a transposon cassette. The ‘target sequence’ is also referred to herein as a “recognition sequence” or “recognition site”. The term “sequence specific endonuclease” is used herein to refer to a DNA endonuclease that binds to and/or ‘recognizes’ the ‘target sequence’ in a target DNA, and cleaves the DNA. In other words, a sequence specific DNA endonuclease recognizes a specific sequence (a recognition sequence) within a target DNA molecule and cleaves the molecule based on that recognition. In some cases the sequence specific DNA endonuclease cleaves the target DNA within the recognition sequence and in some cases it cleaves outside of the recognition sequence (e.g., in the case of type IIS restriction endonucleases).

The term sequence specific DNA endonuclease encompasses, e.g., restriction enzymes, meganucleases, and programmable genome editing nucleases. Thus, examples of sequence specific endonucleases include but are not limited to: restriction endonucleases such as EcoRl, EcoRV, BamHI, etc.; meganucleases such as LAGLIDADG meganucleases (LMNs), I-Scel, I-Ceul, I-Crel, I-Dmol,I-Chul, I-Dirl, I-Flmul, I-Flmull, I-Anil, I-ScelV, I-Csml, I-Panl, I-PanII, I-PanMI, I-Scell, I-Ppol, I-SceIII, I-LtrI, I-GpiI, I-GZeI, I-Onul, I-HjeMI, I-Msol, I-Tevl, I-TevII, I-TevIII, PI-MIel, PI-Mtul, PI-Pspl, PI-Tli I, PI-Tli II, PI-SceV, and the like; and programmable gene editing endonucleases such as Zinc Finger Nucleases (ZFNs), transcription activator like effector nuclease (TALENs), and CRISPR/Cas endonucleases. In some cases, the sequence specific endonuclease of a subject composition and/or method is selected from: a meganuclease and a programmable gene editing endonuclease. In some cases, the sequence specific endonuclease of a subject composition and/or method is selected from: a meganuclease, a ZFN, a TALEN, and a CRISPR/Cas endonuclease (e.g., Cas9, Cpf1, and the like).

In some cases, the sequence specific endonuclease of a subject composition and/or method is a meganuclease. In some cases the meganuclease is selected from: LAGLIDADG meganucleases (LMNs), I-Scel, I-Ceul, I-Crel, I-Dmol, I-Chul, I-Dirt, I-FImul, I-FImull, I-Anil, I-ScelV, I-Csml, I-PanI, I-PanII, I-PanMI, I-Scell, I-Ppol, I-SceIII, I-LtrI, I-GpiI, I-GZeI, I-Onul, I-HjeMI, I-Msol, I-TevI, I-TevII, I-TevIII, PI-MIel, PI-Mtul, PI-Pspl, PI-Tli I, PI-Tli II, and PI-SceV. In some cases, the meganuclease I-Scel is used. In some cases, the meganuclease I-Ceul is used. In some cases, the meganucleases I-Scel and I-Ceul are used.

In some cases the sequence specific DNA endonuclease is a programmable genome editing nuclease. The term “programmable genome editing nuclease” is used herein to refer to endonucleases that can be targeted to different target sites (recognition sequences) within a target DNA. Examples of suitable programmable genome editing nucleases include but are not limited to zinc finger nucleases (ZFNs), TAL-effector DNA binding domain-nuclease fusion proteins (transcription activator-like effector nucleases (TALENs)), and CRISPR/Cas endonucleases (e.g., class 2 CRISPR/Cas endonucleases such as a type II, type V, or type VI CRISPR/Cas endonucleases). Thus, in some embodiments, a programmable genome editing nuclease is selected from: a ZFN, a TALEN, and a CRISPR/Cas endonuclease (e.g., a class 2 CRISPR/Cas endonuclease such as a type II, type V, or type VI CRISPR/Cas endonuclease). In some cases, the sequence specific endonuclease of a subject composition and/or method is a CRISPR/Cas endonuclease (e.g., Cas9, Cpf1, and the like). In some cases, the sequence specific endonuclease of a subject composition and/or method is selected from: a meganuclease, a ZFN, and a TALEN.

Information related to class 2 type II CRISPR/Cas endonuclease Cas9 proteins and Cas9 guide RNAs (as well as methods of their delivery) (as well as information regarding requirements related to protospacer adjacent motif (PAM) sequences present in targeted nucleic acids) can be found in the art, for example, see Jinek et al., Science. 2012 Aug. 17; 337(6096):816-21; Chylinski et al., RNA Biol. 2013 May; 10(5):726-37; Ma et al., Biomed Res Int. 2013; 2013:270805; Hou et al., Proc Natl Acad Sci U S A. 2013 Sep. 24; 110(39):15644-9; Jinek et al., Elife. 2013; 2:e00471; Pattanayak et al., Nat Biotechnol. 2013 Sep.; 31(9):839-43; Qi et al, Cell. 2013 Feb. 28; 152(5):1173-83; Wang et al., Cell. 2013 May 9; 153(4):910-8; Auer et. al., Genome Res. 2013 Oct. 31; Chen et. al., Nucleic Acids Res. 2013 Nov. 1; 41(20):e19; Cheng et. al., Cell Res. 2013 Oct.; 23(10):1163-71; Cho et. al., Genetics. 2013 Nov; 195(3):1177-80; DiCarlo et al., Nucleic Acids Res. 2013 April; 41(7):4336-43; Dickinson et. al., Nat Methods. 2013 Oct; 10(10):1028-34; Ebina et. al., Sci Rep. 2013; 3:2510; Fujii et. al, Nucleic Acids Res. 2013 Nov. 1; 41(20):e187; Hu et. al., Cell Res. 2013 Nov.; 23(11):1322-5; Jiang et. al., Nucleic Acids Res. 2013 Nov. 1; 41(20):e188; Larson et. al., Nat Protoc. 2013 Nov.; 8(11):2180-96; Mali et. at., Nat Methods. 2013 Oct.; 10(10):957-63; Nakayama et. al., Genesis. 2013 December; 51(12):835-43; Ran et. al., Nat Protoc. 2013 November; 8(11):2281-308; Ran et. al., Cell. 2013 Sep. 12; 154(6):1380-9; Upadhyay et. al., G3 (Bethesda). 2013 Dec. 9; 3(12):2233-8; Walsh et. al., Proc Natl Acad Sci U S A. 2013 Sep. 24; 110(39):15514-5; Xie et. al., Mol Plant. 2013 Oct. 9; Yang et. al., Cell. 2013 Sep. 12; 154(6):1370-9; Briner et al., Mol Cell. 2014 Oct. 23; 56(2):333-9; and U.S. patents and patent applications: 8,906,616; 8,895,308; 8,889,418; 8,889,356; 8,871,445; 8,865,406; 8,795,965; 8,771,945; 8,697,359; 20140068797; 20140170753; 20140179006; 20140179770; 20140186843; 20140186919; 20140186958; 20140189896; 20140227787; 20140234972; 20140242664; 20140242699; 20140242700; 20140242702; 20140248702; 20140256046;

20140273037; 20140273226; 20140273230; 20140273231; 20140273232; 20140273233; 20140273234; 20140273235; 20140287938; 20140295556; 20140295557; 20140298547; 20140304853; 20140309487; 20140310828; 20140310830; 20140315985; 20140335063; 20140335620; 20140342456; 20140342457; 20140342458; 20140349400; 20140349405; 20140356867; 20140356956; 20140356958; 20140356959; 20140357523; 20140357530; 20140364333; and 20140377868; all of which are hereby incorporated by reference in their entirety. Examples and guidance related to type V CRISPR/Cas endonucleases (e.g., Cpf1) or type VI CRISPR/Cas endonucleases and guide RNAs (as well as information regarding requirements related to protospacer adjacent motif (PAM) sequences present in targeted nucleic acids) can be found in the art, for example, see Zetsche et al, Cell. 2015 Oct. 22; 163(3):759-71; Makarova et al, Nat Rev Microbiol. 2015 Nov.; 13(11):722-36; and Shmakov et al., Mol Cell. 2015 Nov. 5; 60(3):385-97.

Useful designer zinc finger modules include those that recognize various GNN and ANN triplets (Dreier, et al., (2001) J Biol Chem 276:29466-78; Dreier, et al., (2000) J Mol Biol 303:489-502; Liu, et al., (2002) J Biol Chem 277:3850-6), as well as those that recognize various CNN or TNN triplets (Dreier, et al., (2005) J Biol Chem 280:35588-97; Jamieson, et al., (2003) Nature Rev Drug Discov 2:361-8). See also, Durai, et al., (2005) Nucleic Acids Res 33:5978-90; Segal, (2002) Methods 26:76-83; Porteus and Carroll, (2005) Nat Biotechnol 23:967-73; Pabo, et al., (2001) Ann Rev Biochem 70:313-40; Wolfe, et al., (2000) Ann Rev Biophys Biomol Struct 29:183-212; Segal and Barbas, (2001) Curr Opin Biotechnol 12:632-7; Segal, et al., (2003) Biochemistry 42:2137-48; Beerli and Barbas, (2002) Nat Biotechnol 20:135-41; Carroll, et al., (2006) Nature Protocols 1:1329; Ordiz, et al., (2002) Proc Natl Acad Sci USA 99:13290-5; Guan, et al., (2002) Proc Natl Acad Sci USA 99:13296-301.

For more information on ZFNs and TALENs (as well as methods of their delivery), refer to Sanjana et al., Nat Protoc. 2012 Jan. 5; 7(1):171-92 as well as international patent applications WO2002099084; WO00/42219; WO02/42459; WO2003062455; WO03/080809; WO05/014791; WO05/084190; WO08/021207; WO09/042186; WO09/054985; WO10/079430; and WO10/065123; U.S. Pat. Nos. 8,685,737; 6,140,466; 6,511,808; and 6,453,242; and US Patent Application Nos. 2011/0145940, 2003/0059767, and 2003/0108880; all of which are hereby incorporated by reference in their entirety.

In some cases (e.g., in the case of restriction enzymes), the recognition sequence is a constant (does not change) for the given protein (e.g., the recognition sequence for the BamHl restriction enzyme is G{circumflex over ( )}GATCC). In some cases, the sequence specific DNA endonuclease is ‘programmable’ in the sense that the protein (or its associated RNA in the case of CRISPR/Cas endonucleases) can be modified/engineered to recognize a desired recognition sequence. In some cases (e.g., in cases where the sequence specific DNA endonuclease is a meganuclease and/or in cases where the sequence specific DNA endonuclease is a CRISPR/Cas endonuclease), the recognition sequence has a length of 14 or more nucleotides (nt) (e.g., 15 or more, 16 or more, 17 or more, 18 or more, 19 or more, or 20 or more nt). In some cases the recognition sequence has a length in a range of from 14-40 nt (e.g., 14-35, 14-30, 14-25, 15-40, 15-35, 15-30, 15-25, 16-40, 16-35, 16-30, 16-25, 17-40, 17-35, 17-30, or 17-25 nt). In some cases the recognition sequence has a length of 14 or more base pairs (bp) (e.g., 15 or more, 16 or more, 17 or more, 18 or more, 19 or more, or 20 or more bp). In some cases the recognition sequence has a length in a range of from 14-40 bp (e.g., 14-35, 14-30, 14-25, 15-40, 15-35, 15-30, 15-25, 16-40, 16-35, 16-30, 16-25, 17-40, 17-35, 17-30, or 17-25 bp).

When referring above to the lengths of a recognition sequence, it would be readily understood to one of ordinary skill in the art that some proteins recognize the double-stranded helix and the recognition sequence can therefore be thought of in terms of base pairs (bp), while in some cases (e.g., in the case of CRISPR/Cas endonucleases) the recognition sequence is recognized in single stranded form (e.g., a guide RNA of a CRISPR/Cas endonuclease can hybridize to the target DNA) and the recognition sequence can therefore be thought of in terms of nucleotides (nt). However, when using ‘bp’ or ‘nt’ herein when referring to a recognition sequence, this terminology is not intended to be limiting. As an example, if a particular method or composition described herein encompasses both types of sequence specific DNA endonuclease (those that recognize ‘bp’ and those that recognize ‘nt’), either of the terms ‘nt’ or ‘bp’ can be used without limiting the scope of the sequence specific DNA endonuclease, because one of ordinary skill in the art would readily understand which term (‘nt’ or ‘bp’) would appropriately apply, and would understand that this depends on which protein is chosen. In the case of a length limitation of the recognition sequence, one of ordinary skill in the art would understand that the length limitation being discussed equally applies regardless of whether the term ‘nt’ or ‘bp’ is used.

Chew Back (Exonuclease Digestion)

After the circular target DNAs are cleaved, generating a population of cleaved linear target DNAs, the open ends of the linear target DNAs are digested (chewed back) by exonucleases. Many different exonucleases will be known to one of ordinary skill in the art and any convenient exonuclease can be used. In some cases, a 5′ to 3′ exonuclease is used. In some cases, a 3′ to 5′ exonuclease is used. In some cases, an exonuclease is used that has both 5′ to 3′ and 3′ to 5′ exonuclease activity. In some cases, more than one exonuclease is used (e.g., 2 exonucleases). In some cases, the population of cleaved linear target DNAs is contacted with a 5′ to 3′ exonuclease and a 3′ to 5′ exonuclease (e.g., simultaneously or one before the other).

In some cases, a T4 DNA polymerase is used as a 3′ to 5′ exonuclease (in the absence of dNTPs, T4 DNA polymerase has 3′ to 5′ exonuclease activity). In some cases, RecJ is used as a 5′ to 3′ exonuclease. In some cases T4 DNA polymerase (in the absence of dNTPs) and RecJ are used. Examples of exonucleases include but are not limited to: DNA polymerase (e.g., T4 DNA polymerase) (in the absence of dNTPS), lambda exonuclease (5′->3′), T5 exonuclease (5′->3′), exonuclease III (3′->5′), exonuclease V (5′->3′ and 3′->5′), T7 exonuclease (5′->3′), exonuclease T, exonuclease VII (truncated)(5′->3′), and RecJ exonuclease (5′->3′).

The rate of DNA digestion (chew back) is sensitive to temperature, thus the size of the desired deletion can be controlled by regulating the temperature during exonuclease digestion. For example, in the examples section below when using T4 DNA polymerase (in the absence of dNTPs) and RecJ as the exonucleases, the double-end digestion rate (chewback rate) proceeded at a rate of 50 bp/min at 37° C. and at a reduced rate at lower temperatures (e.g., as discussed in the examples section below). Thus, temperature can be decreased or increased and/or digestion time can be decreased or increased to control the size of deletion (i.e., the amount of exonuclease digestion). For example, in some cases, the temperature and time are adjusted so that exonuclease digestion causes a deletion in a desired size range. As an illustrative example, if a deletion in a range of from 500-1000 base pairs (bp) is desired, the time and temperature of digestion can be adjusted so that 250-500 nucleotides are removed from each end of the linearized (cut) target DNA, i.e., the size of the deletion is the sum of the number of nucleotides removed from each end of the linearized target DNA. In some cases, the temperature and time are adjusted so that exonuclease digestion causes a deletion having a size in a range of from 20-1000 bp (e.g., from 20-50, 40-80, 20-100, 40-100, 20-200, 40-200, 60-100, 60-200, 80-150, 80-250, 100-250, 150-350, 100-500, 200-500, 200-700, 300-800, 400-800, 500-1000, 700-1000, 20-800, 50-1000, 100-1000, 250-1000, 50-1000, 50-750, 100-1000, or 100-750 bp).

In some cases, contacting with an exonuclease (one or more exonucleases) is performed at a temperature in a range of from room temperature (e.g., 25° C.) to 40° C. (e.g., from 25-37° C., 30-37° C., 32-40° C., or 30-40° C.). In some cases contacting with an exonuclease is performed at 37° C. In some cases contacting with an exonuclease is performed at 32° C. In some cases contacting with an exonuclease is performed at 30° C. In some cases contacting with an exonuclease is performed at 25° C. In some cases contacting with an exonuclease is performed at room temperature.

In some cases, the target DNA is contacted with an exonuclease (one or more exonucleases) for a period of time in a range of from 10 seconds to 40 minutes (e.g., from 10 seconds to 30 minutes, 10 seconds to 20 minutes, 10 seconds to 15 minutes, 10 seconds to 10 minutes, 30 seconds to 30 minutes, 30 seconds to 20 minutes, 30 seconds to 15 minutes, 30 seconds to 12 minutes, 30 seconds to 10 minutes, 1 to 40 minutes, 1 to 30 minutes, 1 to 20 minutes, 1 to 15 minutes, 1 to 10 minutes, 3 to 40 minutes, 3 to 30 minutes, 3 to 20 minutes, 3 to 15 minutes, 3 to 12 minutes, or 3 to 10 minutes). In some cases the contacting is for a period of time in a range of from 20 seconds to 15 minutes.

After DNA digestion (chew back), the remaining overhanging DNA ends can be repaired (e.g., using T4 DNA Polymerase plus dNTPs) or in some cases the single stranded overhangs can be removed (e.g., using a nuclease such as mung bean nuclease that cleaves single stranded DNA but not double stranded DNA). For example, if only a 5′ to 3′ or 3′ to 5′ exonuclease is used, a nuclease specific for single stranded DNA (i.e., that does not cut double stranded DNA) (e.g., mung bean nuclease) can be used to remove the overhang.

The step of contacting with one or more exonucleases (i.e., chew back) can be carried out in the presence or absence of a single strand binding protein (SSB protein). An SSB is a protein that binds to exposed single stranded DNA ends, which can achieve numerous results, including but not limited to: (i) helping stabilize the DNA by preventing nucleases from accessing the DNA, and (ii) preventing hairpin formation within the single stranded DNA. Examples of SSB proteins include but are not limited to: a eukaryotic SSB protein (e.g., replication protein A (RPA)); bacterial SSB protein; and viral SSB proteins. In some cases, the step of contacting with one or more exonucleases is performed in the presence of an SSB. In some cases, the step of contacting with one or more exonucleases is performed in the absence of an SSB.

Barcode

In some embodiments, the members of a library are ‘tagged’ by adding a barcode to the target DNAs after exonuclease digestion (and after remaining overhanging DNA ends are repaired/removed). The addition of a barcode can be performed prior to or simultaneously with re-circularizing (ligation). As used herein, term “barcode” is used to mean a stretch of nucleotides having a sequence that uniquely tags members of the library for future identification. For example, in some cases, a barcode cassette (from a pool of random barcode cassettes) can be added and the library sequenced so that it is known which barcode sequence is associated with which particular member, i.e., with which particular deletion (e.g., a lookup table can be created such that each member of a deletion library has a unique barcode). In this way, members of a deletion library can be tracked and accounted for by virtue of presence of the barcode (instead of having to identify the members by determining the location of deletion). As can be readily appreciated, identifying the presence of a short stretch of nucleotides using any convenient assay is much more easily accomplished than attempted to isolate and sequence individual members (in order to determine location of deletion) each time the library is used for a given experiment. For example, one can readily determine which library members are present before an experiment (e.g., before introducing library members into cells to assay for viral infectivity), and compare this to which members are present after the experiment by simply assaying for the presence of the barcode before and after, e.g., using high throughput sequencing, a microarray, PCR, qPCR, or any other method that can detect the presence/absence of a barcode sequence.

In some cases, a barcode is added as a cassette. A barcode cassette is a stretch of nucleotides that have at least one constant region (a region shared by all members receiving the cassette) and a barcode region (i.e., a barcode sequence—a region unique to the members that receive the barcode such that the barcode uniquely marks the members of the library). For example, a barcode cassette can include (i) a constant region that is a primer site, which site is in common among the barcode cassettes used, and (ii) a barcode sequence that is a unique tag, e.g., can be a stretch of random sequence. In some cases, a barcode cassette includes a barcode region flanked by two constant regions (e.g., two different primer sites). As an illustrative example, in some cases a barcode cassette is a 60 bp cassette that includes a 20 bp random barcode flanked by 20 bp primer binding sites (e.g., see FIG. 6).

A barcode sequence can have any convenient length, and is preferably long enough so that it uniquely marks the members of a given library of interest. In some cases, the barcode sequence has a length of from 15 bp to 40 bp (e.g., from 15-35 bp, 15-30 bp, 15-25 bp, 17-40 bp, 17-35 bp, 17-30 bp, or 17-25 bp). In some cases, the barcode sequence has a length of 20 bp. Likewise, a barcode cassette can have any convenient length, and this length depends on the length of the barcode sequence plus the length of the constant region(s). In some cases, the barcode cassette has a length of from 40 bp to 100 bp (e.g., from 40-80 bp, 45-100 bp, 45-80 bp, 45-70 bp, 50-100 bp, 50-80 bp, or 50-70 bp). In some cases, the barcode cassette has a length of 60 bp.

A barcode or barcode cassette can be added using any convenient method. For example, a target DNA can be recircularized by ligation to a 3′-dT-tailed barcode cassette drawn from a pool of random barcode cassettes. The nicked hemiligation product can then be sealed and transformed into a host cell, e.g., a bacterial cell.

Generating a Product

In some cases, a subject method includes a step of generating (e.g., from a generated library of circularized deletion DNAs) at least one of: linear double stranded DNA (dsDNA) products (e.g., via cleavage of the circular DNA, via PCR, etc.), linear single stranded DNA (ssDNA) products (e.g., via transcription and reverse transcription), linear single stranded RNA (ssRNA) products (e.g., via transcription), and linear double stranded RNA (dsRNA) products. If so desired, the linear products can then be introduced into a cell (e.g., mammalian cell). For example, a common technique for RNA viruses like polio, dengue, and Zika is to perform in vitro transcription from a dsDNA template (circular or linear) to make RNA, and then to introduce this RNA into cells (e.g., via electroporation, chemical methods, etc.) to generate viral stocks.

Also within the scope of the disclosure are kits. For example, in some cases a subject kit can include one or more of (in any combination): (i) a population of circular target DNAs as described herein, (ii) a transposon cassette as described herein, (iii) a sequence specific DNA endonuclease as described herein, (iv) one or more guide RNAs for a CRISPR/Cas endonuclease as described herein, (v) a population of barcodes and/or barcode cassettes as described herein, and (vi) a population of host cells, e.g., for propagation of the library, for assaying for viral infectivity, etc., as described herein. In some cases, a subject kit can include instructions for use. Kits typically include a label indicating the intended use of the contents of the kit. The term label includes any writing, or recorded material supplied on or with the kit, or which otherwise accompanies the kit.

Deletion Mutants

The present disclosure provides HIV-1 deletion mutants, e.g., interfering, conditionally replicating, HIV-1 deletion mutants, and related constructs. For example, the present disclosure provides HIV-1 deletion mutants having one or more of the deletions identified in Table 4 relative to the wild type HIV-1 pNL4-3 sequence. The present disclosure also provides HIV deletion mutants having the sequences identified by SEQ ID NOs.: 56-116 in Table 4, e.g., hiv01-hiv60.

More broadly, the present disclosure identifies specific regions of the HIV-1 genome that should be retained and specific regions of the HIV-1 genome that can be deleted in order to provide interfering, conditionally replicating, HIV deletion mutants and related constructs. For example, in order to function as TI Ps, HIV-1 deletion mutants should retain all cis-acting elements. From the high MOI screen described herein with reference to FIGS. 26 and 27, these regions are identified as CAE1 (1115 bp: nt 1-1114 of NL4-3 provirus), CAE2 (126 bp: nt 4779-4905 of NL4-3), CAE3 (671 bp: nt 7710-8381 of NL4-3), and CAE4 (684 bp: nt 9025-9709 of NL4-3). The minimal size/identity of an HIV-1 TIP is a concatenation of these 4 elements (about a 2596 bp provirus). Expressed in common terms used by HIV-1 virologists, CAE1 corresponds to the 5′ LTR through the first 325 bp of gag. CAE2 is the cPPT/CTS. CAE3 is the RRE-SA7 (Rev Response Element to Splice Acceptor 7). CAE4 is the PPT and 5′ LTR.

In addition to retaining cis-acting elements, HIV-1 TI Ps which demonstrate interference with HIV-1 replication should have deletions in at least the gag and/or pol genes. For such TIPs, additional deletions in the accessory tract (vif, vpr, tat (exon 1), rev (exon 1), and/or vpu) may be more interfering than those with an intact accessory tract.

The deletion size for gag and/or pol may range, e.g., from about 800 bp to about 2500 bp, e.g., from about 900 bp to about 2400 bp, from about 1000 bp to about 2300 bp, from about 1100 bp to about 2200 bp, from about 1200 bp to about 2100 bp, from about 1300 bp to about 2000 bp, from about 1400 bp to about 1900 bp, from about 1500 bp to about 1800 bp, or from about 1600 bp to about 1700 bp.

In some embodiments, the deletion size for gag and/or pol may range from about 900 bp to about 2500 bp, from about 1000 bp to about 2500 bp, from about 1100 bp to about 2500 bp, from about 1200 bp to about 2500 bp, from about 1300 bp to about 2500 bp, from about 1400 bp to about 2500 bp, from about 1500 bp to about 2500 bp, from about 1600 bp to about 2500 bp, from about 1700 bp to about 2500 bp, from about 1800 bp to about 2500 bp, from about 1900 bp to about 2500 bp, from about 2000 bp to about 2500 bp, from about 2100 bp to about 2500 bp, from about 2200 bp to about 2500 bp, from about 2300 bp to about 2500 bp, or from about 2400 bp to about 2500 bp.

In some embodiments, the deletion size for gag and/or pol is about 800 bp, about 900 bp, about 1000 bp, about 1100 bp, about 1200 bp, about 1300 bp, about 1400 bp, about 1500 bp, about 1600 bp, about 1700 bp, about 1800 bp, about 1900 bp, about 2000 bp, about 2100 bp, about 2200 bp, about 2300 bp, about 2400 bp, or about 2500 bp.

The deletion size for the accessory tract (vif, vpr, tat (exon 1), rev (exon 1), and/or vpu) may range, e.g., from about 900 bp to about 1300 bp, e.g., from about 1000 bp to about 1200 bp, such as about 1100 bp. In some embodiments, the deletion size for the accessory tract (vif, vpr, tat, rev, and/or vpu) may range from about 1000 bp to about 1300 bp, e.g., from about 1100 bp to about 1300 bp, or from about 1200 bp to about 1300 bp. In some embodiments, the deletion size for the accessory tract (vif, vpr, tat (exon 1), rev (exon 1), and/or vpu) is about 900 bp, about 1000 bp, about 1100 bp, about 1200 bp, or about 1300 bp.

HIV-1 TI Ps which demonstrate interference with HIV-1 replication may also include, e.g., in addition to a deletion in gag and/or pol, a deletion in nef. Such a deletion may be, e.g., from about 150 bp to about 200 bp, e.g., about 175 bp.

Exemplary Non-Limiting Aspects of the Disclosure

Aspects, including embodiments, of the present subject matter described above may be beneficial alone or in combination, with one or more other aspects or embodiments. Without limiting the foregoing description, certain non-limiting aspects of the disclosure numbered 1-56 are provided below. As will be apparent to those of ordinary skill in the art upon reading this disclosure, each of the individually numbered aspects may be used or combined with any of the preceding or following individually numbered aspects. This is intended to provide support for all such combinations of aspects and is not limited to combinations of aspects explicitly provided below:

-   1. A method of generating a deletion library, comprising:

(a) inserting a transposon cassette comprising a target sequence for a sequence specific DNA endonuclease into a population of circular target DNAs to generate a population of transposon-inserted circular target DNAs;

(b) contacting the population of transposon-inserted circular target DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear target DNAs;

(c) contacting the population of cleaved linear target DNAs with one or more exonucleases to generate a population of deletion DNAs; and (d) circularizing the deletion DNAs to generate a library of circularized deletion DNAs.

-   2. The method of 1, wherein the circular target DNAs are plasmids     that comprise a viral genome. -   3. The method of 2, wherein the method further comprises introducing     members of the library of circularized deletion DNAs into mammalian     cells, and assaying for viral infectivity. -   4. The method of 2 or 3, wherein the method further comprises     sequencing members of the library of circularized deletion DNAs to     identify defective interfering particles (DIPs). -   5. The method of any one of 1-4, wherein the sequence specific DNA     endonuclease is selected from: a meganuclease, a CRISPR/Cas     endonuclease, a zinc finger nuclease, or a TALEN. -   6. The method of any one of 1-5, wherein the method comprises     inserting a barcode sequence prior to or simultaneous with step (d). -   7. The method of any one of 1-6, wherein the one or more     exonucleases comprises T4 DNA polymerase. -   8. The method of any one of 1-7, wherein the one or more     exonucleases comprises a 3′ to 5′ exonuclease and a 5′ to 3′     exonuclease. -   9. The method of any one of 1-8, wherein the one or more     exonucleases comprises RecJ. -   10. The method of any one of 1-9, wherein the step of contacting the     population of cleaved linear target DNAs with one or more     exonucleases is performed in the presence of a single strand binding     protein (SSB). -   11. The method of any one of 1-10, wherein the transposon cassette     comprises a first recognition sequence positioned at or near one end     of the transposon cassette and a second recognition sequence     positioned at or near the other end of the transposon cassette. -   12. The method of any one of 1-11, further comprising, prior to step     (a), circularizing a population of linear DNA molecules to generate     said population of circular target DNAs. -   13. The method of 12, wherein the population of linear DNA molecules     comprises one or more PCR products, one or more linear viral     genomes, and/or one or more restriction digest products. -   14. The method of any one of 1-13, further comprising introducing     members of the library of circularized deletion DNAs into mammalian     cells. -   15. The method of any one of 1-13, further comprising generating     from the library of circularized deletion DNAs, at least one of:     linear double stranded DNA (dsDNA) products, linear single stranded     DNA (ssDNA) products, linear single stranded RNA (ssRNA) products,     and linear double stranded RNA (dsRNA) products. -   16. The method of 15, further comprising introducing said linear     dsDNA products, linear ssDNA products, linear ssRNA products, and/or     linear dsRNA products into mammalian cells. -   17. A method of generating and identifying a defective interfering     particle (DIP), comprising:

(a) inserting a target sequence for a sequence specific DNA endonuclease into a population of circular target viral DNAs, each comprising a viral genome, to generate a population of sequence-inserted viral DNAs;

(b) contacting the population of sequence-inserted viral DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear viral DNAs;

(c) contacting the population of cleaved linear viral DNAs with an exonuclease to generate a population of deletion DNAs;

(d) circularizing the deletion DNAs to generate a library of circularized deletion viral DNAs; and

(e) sequencing members of the library of circularized deletion viral DNAs to identify deletion interfering particles (DIPs).

-   18. The method of 17, comprising, prior to step (a), circularizing a     population of linear DNA molecules to generate said population of     circular target viral DNAs. -   19. The method of 18, wherein the population of linear DNA molecules     comprises one or more PCR products, one or more linear viral     genomes, and/or one or more restriction digest products. -   20. The method of any one of 17-19, wherein the method comprises     inserting a barcode sequence prior to or simultaneous with step (d). -   21. The method of any one of 17-20, further comprising (i)     introducing members of the library of circularized deletion viral     DNAs into mammalian cells; and (ii) assaying for viral infectivity. -   22. The method of any one of 17-20, further comprising:

(i) generating from the library of circularized deletion viral DNAs, at least one of: linear double stranded DNA (dsDNA) products, linear single stranded DNA (ssDNA) products, linear single stranded RNA (ssRNA) products, and linear double stranded RNA (dsRNA) products.

-   23. The method of 22, further comprising, after step (i):

(ii) introducing said linear dsDNA products, linear ssDNA products, linear ssRNA products, and/or linear dsRNA products into mammalian cells; and

(iii) assaying for viral infectivity.

-   24. The method of any one of 12-14, wherein the inserting of     step (a) comprises inserting a transposon cassette into the     population of circular target viral DNAs, wherein the transposon     cassette comprises the target sequence for the sequence specific DNA     endonuclease, and wherein said generated population of     sequence-inserted viral DNAs is a population of transposon-inserted     viral DNAs. -   25. The method of any one of 17-24, wherein the method comprises,     after step (d), infecting mammalian cells in culture with members of     the library of circularized deletion viral DNAs at a high     multiplicity of infection (MOI), culturing the infected cells for a     period of time ranging from 12 hours to 2 days, adding naive cells     to the to the culture, and harvesting virus from the cells in     culture. -   26. The method of any one of 17-25, wherein the method comprises,     after step (d), infecting mammalian cells in culture with members of     the library of circularized deletion viral DNAs at a low     multiplicity of infection (MOI), culturing the infected cells in the     presence of an inhibitor of viral replication for a period of time     ranging from 1 day to 6 days, infecting the cultured cells with     functional virus at a high MOI, culturing the infected cells for a     period of time ranging from 12 hours to 4 days, and harvesting virus     from the cultured cells. -   27. A transposon cassette, comprising a DNA molecule comprising     transposase compatible inverted terminal repeats (ITRs) flanking a     sequence of interest, wherein the sequence of interest comprises a     first copy and a second copy of a recognition sequence for a first     meganuclease. -   28. The transposon cassette of 27, wherein the sequence of interest     includes a selectable marker gene, and said first and second copies     flank the selectable marker gene. -   29. The transposon cassette of 28, wherein the selectable marker     gene encodes an antibiotic resistance protein. -   30. The transposon cassette of any one of 27-29, comprising a first     copy and a second copy of a recognition sequence for a second     meganuclease. -   31. The transposon cassette of 30, wherein the first and second     copies of the recognition sequence for the second meganuclease flank     a selectable marker gene. -   32. The transposon cassette of any one of 27-31, wherein the     transposase compatible inverted terminal repeats (ITRs) are cable of     being recognized and utilized by a Tn5 transposase. -   33. An HIV-1 deletion mutant construct comprising all cis-acting     elements of HIV-1 (CAE1 (1115 bp: nt 1-1114 of NL4-3 provirus), CAE2     (126 bp: nt 4779-4905 of NL4-3), CAE3 (671 bp: nt 7710-8381 of     NL4-3), and CAE4 (684 bp: nt 9025-9709 of NL4-3)) and a deletion in     the gag and/or pol genes. -   34. The HIV-1 deletion mutant construct of 33, wherein the construct     comprises a deletion in one or more of the vif, vpr, tat, rev,     and/or vpu genes. -   35. The HIV-1 deletion mutant construct of 33 or 34, wherein the     deletion in the gag and/or pol genes is from about 800 bp to about     2500 bp in length. -   36. The HIV-1 deletion mutant construct of any one of 33-35, wherein     the deletion in one or more of the vif, vpr, tat, rev, and/or vpu     genes is from about 900 bp to about 1300 bp in length. -   37. The HIV-1 deletion mutant construct of any one of 33-36,     comprising a deletion in the nef gene. -   38. The HIV-1 deletion mutant construct of 37, wherein the deletion     in the nef gene is about 150 bp to about 200 bp in length. -   39. The HIV-1 deletion mutant construct of any one of 33-38,     comprising one or more of the deletions identified in Table 4     relative to the wild type HIV-1 NL4-3 proviral sequence. -   40. The HIV-1 deletion mutant construct of any one of 33-39, wherein     the construct does not include any heterologous nucleic acid     sequence that encode a gene product. -   41. An HIV-1 deletion mutant construct comprising the nucleic acid     sequence set forth in any one of the SEQ ID NOs. 56-116 set forth in     Table 4. -   41(b). The HIV-1 deletion mutant construct of 41, wherein the     construct is not replication competent and interferes with the     replication of a wildtype HIV-1 virus, e.g., as identified in Table     9. -   42. A particle comprising:

a) an HIV-1 deletion mutant construct of any one of 33-41; and

b) a viral envelope protein.

-   43. The particle of 41, wherein the envelope protein comprises     gp120. -   44. The particle of 41, wherein the envelope protein is a non-HIV     protein. -   45. A pharmaceutical formulation comprising:

a) the particle of any one of 42-44, or a particle comprising the construct according to any one 33-41; and

b) a pharmaceutically acceptable excipient.

-   46. A package for use in delivering the construct of one of 33-41 to     an individual, the package comprising a container comprising the     formulation of 45. -   47. The package of 46, wherein the container is a syringe. -   48. A method of reducing human immunodeficiency virus viral load in     an individual, the method comprising administering to the individual     an effective amount of a pharmaceutical formulation of 45. -   49. The method of 48, further comprising administering to the     individual an effective amount of an agent that inhibits an     immunodeficiency virus function selected from viral replication,     viral protease activity, viral reverse transcriptase activity, viral     entry into a cell, viral integrase activity, viral Rev activity,     viral Tat activity, viral Nef activity, viral Vpr activity, viral     Vpu activity, and viral Vif activity.

50. The method of 48 or 49, wherein the individual has been diagnosed with an HIV infection.

-   51. The method of 48 or 49, wherein the individual is considered to     be at higher risk than the general population of becoming infected     with HIV. -   52. The method of any one of 48-51, further comprising administering     to the individual an effective amount of an agent that reactivates     reactivating latent HIV integrated into the genome of a cell     infected with HIV. -   53. A biological fluid comprising the construct of any one of 33-41     or a derivative thereof. -   54. The biological fluid of 53, wherein the biological fluid is     plasma. -   55. A method of generating a variant HIV-1 deletion mutant     construct, the method comprising:

a) introducing the construct of any one of 33-41 into a first individual;

b) obtaining a biological sample from a second individual to whom the construct of any one of 33-41has been transmitted from the first individual, wherein the construct present in the second individual is a variant of the construct of any one of 33-41; and

c) cloning the variant construct from the second individual.

-   56. The HIV-1 deletion mutant construct of any one 33-41, wherein     genomic RNA encoded by the construct is produced at a higher rate     than wild-type HIV when present in a host cell infected with a     wild-type HIV, such that the ratio of construct-encoded gRNA to     wild-type HIV gRNA is higher than about 1 in the cell, and wherein     the construct has a basic reproductive ratio (R₀)>1.

It will be apparent to one of ordinary skill in the art that various changes and modifications can be made without departing from the spirit or scope of the invention.

EXPERIMENTAL

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of the invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric.

All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference.

The present invention has been described in terms of particular embodiments found or proposed to comprise preferred modes for the practice of the invention. It will be appreciated by those of skill in the art that, in light of the present disclosure, numerous modifications and changes can be made in the particular embodiments exemplified without departing from the intended scope of the invention. For example, due to codon redundancy, changes can be made in the underlying DNA sequence without affecting the protein sequence. Moreover, due to biological functional equivalency considerations, changes can be made in protein structure without affecting the biological action in kind or amount. All such modifications are intended to be included within the scope of the appended claims.

Method to Produce a Deletion Library

The following examples demonstrate a high-throughput, molecular biology method, which used cycles of in vitro transposition and exonuclease digestion to generate random deletions in circular DNA (FIG. 1). The method allows control over the size of random deletions and optionally tags each member of the library with a molecular barcode to facilitate analysis by sequencing. The examples provided below demonstrate the generation of a library of tagged viral mutants. Performing multiple iterations of the cycle allows for the generation of multiply-deleted strains.

Materials and Methods (for Examples 1-5) Determination of Minimal Conditions for Chewback Reactions (λ-HindII Digest)

Chewback reactions were conducted in NEB Buffer 2.1 (New England Biolabs), the composition of which at lx concentration is:

50 mM NaCl

10 mM Tris-Cl

10 mM MgCl2

100 ug/ml BSA

pH 7.9 @ 25° C.

λ DNA-HindIII digest, T4 DNA Polymerase (3 U/μl), RecJ_(f)(30 U/μl), and ET SSB (500 ng/μl), were obtained from New England Biolabs. Template DNA, λ DNA-HindIII digest (New England Biolabs, #N3012S), was prepared for chewback by heating to 60° C. for 3 min and immediately cooling on wet ice prior to addition to the chewback reaction to separate annealed cohesive cos ends.

A standard 50 μl chewback reaction was prepared on wet ice in a 0.2 ml PCR tube by combining:

30.3 μl of dH₂O

5.0 μl of 10X NEB 2.1

10.0 μl of A DNA-HindIII digest (500 ng/μl)

1.7 μl of T4 DNA Polymerase (3 U/μl)

0.5 μl of RecJ_(f)(30 U/μl)

0.5 μl of ET SSB (500 ng/μl)

The 50 μl reaction was immediately transferred from wet ice to a thermocycler (Bio-Rad) set to a block temperature of 37° C. and a heated lid temperature of 50° C., and incubated at 37° C. for 30 minutes to effect the double-strand chewback. After 30 minutes, 1 μl of 10 mM dNTPs was added (200 uM final dNTP concentration) and the reaction mixed and returned to 37° C. for 11 min to allow T4 DNA Polymerase to fill in recessed ends. After 11 minutes of fill-in, the reaction was halted by adding 2 μl of (500 mM EDTA, pH 8.0) to bring the EDTA concentration to 20 mM.

For the various dropout reactions depicted in FIG. 7, dH₂O was substituted for enzyme solutions. Lane 1: 0 μl enzyme, Lane 2: 1.7 μl T4 DNA Pol, Lane 3: 1.7 μl T4 DNA Pol, 0.5 μl ET SSB, Lane 4: 1.7 μl T4 DNA Pol, 0.5 μl RecJ_(f) , Lane 5: 1.7 μl T4 DNA Pol, 0.5 μl RecJ, 0.5 μl ET SSB.

Determination of Chew-Back Rate

A ˜4.3 kbp dsDNA template was obtained by purifying the 4361 bp fragment of λ DNA-HindIII digest. Ten μg of λ DNA-HindIII digest (New England Biolabs, #N3012S) were run out on a 0.8% low melting point agarose/TAE gel (Lonza SeaPlaque GTG agarose) and the gel stained for 20 minutes at 25° C. with SYBR Safe (Thermo Fisher Scientific) diluted to lx concentration in TAE. DNA bands were visualized by placing the gel atop a blue light transilluminator (Lonza) and viewing the illuminated gel through UVEX S0360X blue light blocking safety glasses (Honeywell). Gel slices corresponding to the 4361 bp fragment were excised with a clean single-edge safety razor blade and transferred to tared microcentrifuge tubes. DNA was recovered by adding 0.1 gel volumes of 10× β-agarase I reaction buffer (New England Biolabs), melting gel slices briefly at 65° C., cooling to 42° C., and immediately adding 1 U of β-agarase I per 100 μl of molten gel (New England Biolabs). The mixture was incubated at 42° C. for 60 min to release DNA bound in the agarose matrix. DNA was precipitated from the digested fraction of the agarase reaction by adding 0.1 volumes of 3 M sodium acetate, pH 5.4, and 2 reaction volumes of 2-propanol. After mixing, the reaction was spun at 20000xg for 15 minutes at 25° C., and the supernatant aspirated. The DNA pellet was washed once with 900 μl of 70% ethanol, allowed to air dry briefly, then dissolved in (10 mM Tris-Cl, pH 8.0; 0.1 mM EDTA, pH 8.0).

200 μl of 2XdNTP buffer were prepared by combining:

40 μl of 10X NEB 2.1 (2X final conc.)

8 μl of 10 mM dNTP (400 μM final conc.)

152 μl of dH₂O

and stored on wet ice. 150 μl of Stop Buffer was prepared by combining

10 μl of 500 mM EDTA, pH 8.0 (33 mM final conc.)

140 μl of dH2O

and stored at bench temperature (24 C). A 50 μl chew-back reaction was prepared on wet ice in a 0.2 ml PCR by combining:

30.3 μl of dH₂O

5 μl of 10X NEB 2.1

12 μl of 4.3 kbp dsDNA from above (-25 ng/μl)

1.7 μl of T4 DNA Polymerase (3 U/μl)

0.5 μl of RecJf (30 U/μl)

0.5 μl of ET SSB (500 ng/μl)

The 50 μl reaction was immediately transferred to a thermocycler set to a block temperature of 37° C. and a lid temperature of 95° C. At (0, 5,10, 15, 20, 25, 30, 40, 50, 60, 70, 80 min) post-transfer to 37° C., a 4 μl aliquot was removed and combined with 4 μl of 2X dNTP buffer. These 8 μl reactions were incubated at 37° C. for 11 minutes to allow T4 DNA Polymerase to fill in the single-stranded tails that remain uncleaved by RecJ_(f). After 11 minutes of fill-in, the reaction was halted by adding 12 μl of Stop Buffer to bring the EDTA concentration to 20 mM. Reactions were incubated on wet ice after addition of 12 μl of Stop Buffer.

dsDNA concentration was determined by a fluorometric method (PicoGreen, Thermo Fisher Scientific). 5 μl of each reaction was added to 95 μl of TE 10/1, pH 7.5. To this, 100 μl of a PicoGreen working stock (diluted to 1/200× in TE 10/1) were added in an Opti-F (Perkin Elmer) plate and read with an Enspire plate reader (Perkin Elmer) with 480 nm excitation and 520 emission filter, and fluorescence compared to a A DNA standard. All reactions were performed in triplicate.

Chewback rates at 37° C. were calculated by fitting the decay in dsDNA (fluoresence signal) at various timepoints to a linear regression model with the freely-available R statistical software. Chewback rates were determined to be ˜60 bp/min for 0-20 min and ˜50 bp/min for 0-80 min.

Production of Transposon Insertion Library

Linear transposon cassettes were constructed by PCR from pTN5MK plasmid template. Oligos oTN5-F (5′-ctgtctcttatacacatctgcggccgc-3′) (SEQ ID NO: 15) and oTN5-R (5′-ctgtctcttatacacatctgcggccgc-3′) (SEQ ID NO: 16) were ordered with covalent 5′-phosphorylation modification and standard desalting purification from Integrated DNA Technologies. A 300 μl PCR master mix was prepared by mixing the following at bench temperature (24° C.):

60 μl of 5x Q5 Polymerase Buffer (New England Biolabs)

171 μl of dH₂O

6 μl of 10 mM dNTP

30 μl of 6 μM oTN5-F

30 μl of 6 μM oTN5-R

6 μl of pTN5MK (1 ng/μl)

3 μl of HotStart Q5 Polymerase (2 U/μl) (New England Biolabs)

The 300 μl PCR master mix was briefly mixed, then distributed as 6×50 μl aliquots in 0.2 ml PCR tubes. PCR was performed using the following program in a thermocycler with heated lid (105° C.):

1 cycle of 98° C. for 30 s

15 cycles of

-   -   98° C. for 10 s     -   68° C. for 20 s     -   72° C. for 50 s

1 cycle of 72° C. for 300 s

HOLD at 10° C.

Post-thermocycling, the 6×50 μl reactions were pooled and linear transposon DNA purified with the Zymo DCC-5 Kit (Zymo Research) across two DCC-5 silica columns per the manufacturer's instructions. The DNA was eluted from each column by adding 12 μl of (10 mM Tris-Cl pH 8.0; 0.1 mM EDTA, pH 8.0), and the two eluted fractions were pooled to obtain ˜20 μl of purified transposon product. The concentration of linear DNA was determined to be ˜75 ng/μl by absorbance at 260 nm using a Nanodrop spectrophotometer (Thermo Fisher Scientific).

The ˜1.4 kbp linear transposon DNA was gel-purified by running out all 20 μl in a 2-cm wide well in a 0.8% agarose/TAE gel. Post-run, the gel was stained with 1X SYBR Safe (Thermo Fisher Scientific) in 1x TAE and a gel fragments corresponding to the 1.4 kbp linear transposon fragment excised upon illumination with a blue light transilluminator (Lonza) and viewed through UVEX S0360X blue light blocking safety glasses (Honeywell). DNA was recovered from the gel slice by adding 3 gel volumes of Buffer QG (Qiagen), and melting the gel slice by incubation at 37° C. with frequent mixing. The liquid gel mixture was applied to a DCC-5 silica column (Zymo Research) in repeated 600 μl volumes, interspersed by spinning the column at 10000xg for 40 seconds and discarding the flowthrough. The DCC-5 column was washed twice by adding 600 μl of Wash Buffer (Zymo Research), spinning the column at 10000xg for 60 seconds, and discarding the flow-though. The column was carefplly transferred to a 1.5 ml DNA LoBind tube (Eppendorf) and 30 μl of (10 mM Tris-Cl pH 8.0; 0.1 mM EDTA, pH 8.0) applied to the column bed and incubated for 1 minute. DNA was eluted by spinning the column for 1 minute at 10000xg . The concentration of linear DNA was found to be -30 ng/μl by determining the absorbance at 260 nm using a Nanodrop spectrophotometer (Thermo Fisher Scientific).

An in vitro transposition reaction was performed using recombinant EZ-Tn5 transposase (Epicentre) (at a concentration of 1 U/μl in 50% glycerol containing 50 mM Tris-HCl (pH 7.5), 0.1 M NaCI, 0.1 mM EDTA, 1 mM dithiothreitol, and 0.1% Triton® X-100) and 10X EZ-Tn5 reaction buffer (Epicentre) (composition: 0.50 M Tris-acetate (pH 7.5), 1.5 M potassium acetate, 100 mM magnesium acetate, and 40 mM spermidine).

A 10 μl in vitro transposition reaction was assembled by combining the following in a 0.2 ml PCR tube:

2.0 μl of pNL4-3 (100 ng/μl) [14825 bp] [21.83 fmol]

2.0 μl of TN5MK gel-purified transposon (10 ng/μl) [1434 bp] [22 fmol]

1.0 μl of 10X EZ-Tn5 reaction buffer

4.0 μl of dH2O

1.0 μl of EZ-Tn5 transposase (1U/μl)

The reaction was mixed and the 0.2 ml PCR tube transferred to a thermocycler set to a block temperature of 37° C. and a heated lid temperature of 50° C. for a 2 hour incubation. After a 2 hour incubation, 1 μl of 1% (m/v) SDS solution was added and the reaction heated to 70° C. for 10 min to halt the reaction.

After equilibrating to room temperature, the entire volume of the reaction was pipetted upon a 0.025 μm membrane (13 mm outer diameter) (Millipore, #VSWP01300), floating on 25 ml of TE 10/0.1, pH 8.0. Drop-dialysis was allowed to proceed for 1 hour to remove inhibitory salts from the reaction mixture. After 1 hour the reaction volume was recovered and placed in a DNA LoBind tube (Eppendorf) on ice.

1 μl of the reaction mixture (˜10%) was added to 40 μl of ice-cold electrocompetent E. coli (strain DH10B), and introduced into a chilled 0.1-cm sterile cuvette (Bio-Rad) placed on wet ice. Bacteria were electroporated with a Gene Pulser II electroporation system (Bio-Rad) with pulse settings of 1.7 kV, 25 μF, 200 Ω. Immediately post-electroporation, 960 μl of SOC (Thermo Fisher) were added and the cell mixture transferred to a sterile 15 ml polypropylene conical tube, and allowed to recover for 90 minutes at 30° C. After a 90 min recovery, 10 μl (1%) of the reaction was plated on one 10-cm plates containing solid media comprised of

Lysogeny Broth supplemented with 1% agar, 100 μg/mI carbenicillin, and 50 μg/mI kanamycin (LBA+Carb₁₀₀+Kan₅₀). The remaining 99% of the transformation volume was plated across 6×10-cm LBA+Carb₁₀₀ +Kan₅₀ plates. After incubation for 24 hours at 32° C., approximately 5000-10000 CFU were obtained across the six library plates. The bacteria were scraped from the agar surface using a sterile cell spreader after adding 5 ml of LB to each plate and recovered by centrifugation at 4000xg for 15 minutes. The bacterial pellet was resuspended in 6 ml of LB supplemented with 7% (v/v) DMSO and stored in 1.0 ml cryovials at −80° C. for future use.

Production of a Barcoded Deletion Library from an Insertion Library

One vial of the frozen insertion library (TN5MK in pNL4-3) was thawed and used to inoculate 500 ml of LB-Miller supplemented with 100 μg/ml carbenicillin and 50 μg/ml kanamycin (LBM+Carb₁₀₀+Kan₅₀) in a 2.8 L Fernbach flask. The culture was grown at 30° C. and 250 rpm in a shaking incubator (New Brunswick Scientific) until it reached an OD₆₀₀ of 1.0, whereupon a dry bacterial pellet was obtained by centrifugation and frozen at −80° C. Supercoiled plasmid DNA was obtained from the frozen bacterial pellet with a DNA Maxiprep Kit (Qiagen) per the manufacturer's instructions, and resuspended in TE 10/0.1 (10 mM Tris-Cl, pH 8.0; 0.1 mM EDTA, pH 8.0) at a concentration of >200 ng/μl.

Next, inserted transposons were excised from the plasmid insertion library to create linear DNA molecules by treatment with meganuclease I-Scel (New England Biolabs) in lx CutSmart Buffer (New England Biolabs), whose 1X composition as specified by the manufacturer is (50 mM potassium acetate, 20 mM Tris-acetate, 10 mM magnesium acetate, 1 mM DTT, 100 μg/ml BSA, pH 7.9 at 25° C.), by the manufacturer (New England Biolabs). Approximately 50 μg of insertion library DNA were digested in a 500 μl reaction by mixing the following in DNA LoBind tube (Eppendorf):

105 μl of TN5MK in pNL4-3 (485 ng/μl)

50 μl of 10X CutSmart Buffer (New England Biolabs)

20 μl of I-Scel (5U/μl)

335 μl of dH₂O

The reaction was incubated for 8 hours at 37° C., with brief mixing by inversion performed every 2 hours. After 8 hours, the reaction was cooled to bench temperature (24° C.), then extracted once with 500 μl of 25:24:1 phenol:chloroform:isoamyl alcohol equilibrated with TE, pH 8.0 (Thermo Fisher Scientific) followed by a second extraction with 500 μl of pure chloroform (Sigma). The upper aqueous layer was transferred to a new DNA LoBind tube, and 1.0 μl (25 μg) of co-precipitating GenElute Linear Polyacrylamide (Sigma) was added and the solution mixed to homogeneity.

Digested DNA was precipitated from the aqueous phase by MgCl₂/PEG-8000 precipitation. The ˜500 μl were adjusted to a final concentration of 12.5% (m/v) PEG-8000 and 20 mM MgCl₂ by adding 14 μl of 1 M MgCl₂ and 168 μl of 50% (m/v) PEG-8000. The reaction was inverted and flicked to mix, then spun at 20000xg for 60 min in a refrigerated microcentrifuge (Eppendorf) at 25° C. to pellet the precipitated DNA. After centrifugation, the pellet was difficult to visualize. The supernatant was removed and discarded and 900 μl of freshly-prepared 70% ethanol were added and the tube contents mixed by inverting the tube and flicking. Upon addition of 70% ethanol, the DNA pellet became readily visible. The tube was spun at 20000xg for 2 min to collect the pellet and the supernatant aspirated and discarded. An additional 900 μl of 70% ethanol were added to wash the pellet, and the tube spun again at 20000xg for 2 min to collect the pellet. All supernatant was carefully removed and the pellet dried briefly at room temperature (5 min) until no visible liquid remained. The DNA was solubilized by adding 60 μl of TE 10/0.1, heating to 42° C. for 20 minutes and mixed by flicking the tube. The concentration of linear DNA was found to be ˜750 ng/μl by a fluorometric assay (Quant-iT™ PicoGreen® dsDNA Assay Kit from Thermo Fisher Scientific). DNA was stored at 4° C. until future use.

Before the chewback reaction occurred, substrate DNA was heated to 60° C. for 3 minutes and immediately placed on wet ice to separate DNA aggregates. Four standard chewback reactions (reactions R5, R10, R15, R20) were prepared on wet ice in four separate 0.2 ml PCR tubes. Each reaction was prepared by combining the following in a separate 0.2 ml PCR tube:

5.0 μl of 10X NEB 2.1

36.3 μl of dH₂O

6.0 μl of linearized pNL4-3/TN5MK insertion lib. (750 ng/μl)

1.7 μl of T4 DNA Polymerase (3 U/μl)

0.5 μl of RecJ_(f) (30 U/μl)

0.5 μl of ET SSB (500 ng/μl)

All four 50 μl reactions were immediately transferred from wet ice to a thermocycler (Bio-Rad) set to a block temperature of 37° C., a heated lid temperature of 50° C., then incubated at 37° C. for a duration of 5-20 minutes to effect the double-strand chewback (R5: 5 min, R10: 10 min, R15: 15 min, R20: 20 min). At the appropriate time, the indicated reaction was removed from 37° C. incubation and 1 μl of 10 mM dNTPs were added (200 μM final dNTP concentration). The reaction was mixed and returned to 37° C. for 11 min to allow T4 DNA Polymerase to fill in recessed ends. After 11 minutes of fill in, the reaction was halted by adding 2 μl of (500 mM EDTA, pH 8.0) to adjust the EDTA concentration to 20 mM and placed on wet ice.

All four 50 μl chewback reactions (R5,R10,R15,R20) were pooled (200 μl volume) and then extracted once with 200 μl of 25:24:1 phenol:chloroform:isoamyl alcohol equilibrated with TE, pH 8.0, (Thermo Fisher Scientific). The ˜200 μl upper aqueous layer was transferred to a new DNA LoBind tube (Eppendorf), and desalted by running 2×100 μl through separate Sephacryl gel filtration columns (Microspin S-400 HR columns (GE Lifesciences)).

The 2×100 μl flowthrough fractions were pooled and the linear DNA blunt-ended by NEBNext End Repair Reaction Module (New England Biolabs). The composition of the 1X End Repair Reaction buffer is specified by the manufacturer as: 50 mM Tris-HCI, 10 mM MgCl₂, 10 mM DTT, 1 mM ATP, 0.4 mM dATP, 0.4 mM dCTP, 0.4 mM dGTP, 0.4 mM dTTP, pH 7.5 at 25° C.). The enzyme mix contains a blend of T4 Polynucleotide Kinase (10 U/μl) and T4 DNA Polymerase (3 U/μl). A 400 μl end-repair reaction was prepared by combining the following in a DNA LoBind tube (Eppendorf) on wet ice:

200 μl of linearized deletion library (˜20 μg total)

40 μl of 10X End Repair Buffer (NEB)

140 μl of dH₂O

20 μl of EndRepair Enzyme Mix (NEB)

The 400 μl reaction was distributed as 2×200 μl aliquots in 0.2 ml PCR tubes and incubated for 30 minutes in a thermocycler (Bio-Rad) with a block temperature set to 20° C.

After the 30 minute incubation, the 2×200 μl fractions were pooled and a single DNA LoBind tube (Eppendorf). The 400 μl pool was extracted once with 400 μl of 25:24:1 phenol:chloroform:isoamyl alcohol equilibrated with TE 10/1, pH 8.0, (Thermo Fisher Scientific), and once with 400 μl of pure chloroform (Sigma). The upper aqueous phase was transferred to a new DNA LoBind tube, and 1.0 μl (25 μg) of co-precipitating GenElute Linear Polyacrylamide (Sigma) was added and the solution mixed to homogeneity.

DNA was precipitated by MgCl₂/PEG-8000 precipitation. The remaining ˜400 μl aqueous phase volume remaining was adjusted to a final concentration of 12.5% (m/v) PEG-8000 and 20 mM MgCl₂ by adding 13 μl of 1 M MgCl₂ and 135 μl of 50% (m/v) PEG-8000. The reaction was inverted and flicked to mix, then spun at 20000xg for 60 min in a refrigerated microcentrifuge (Eppendorf) at 25° C. to pellet the precipitated DNA. After centrifugation, the pellet was translucent and difficult to visualize. The supernatant was removed and discarded and 900 μl of freshly-prepared 70% ethanol were added and the tube mixed. Upon addition of 70% ethanol, the DNA pellet became white, opaque, and was readily visible. The tube was spun at 20000xg for 2 min to collect the pellet and the supernatant aspirated and discarded. An additional 900 μl of 70% ethanol were added to wash the pellet, and the tube spun at 20000xg for 2 min to collect the pellet. All supernatant was carefully removed and the pellet dried briefly at room temperature (5 min) until no visible liquid remained. The DNA was solubilized by adding 60 μl of TE 10/0.1, heating to 42° C. for 20 minutes and mixed by flicking the tube. The concentration of linear DNA was found to be ˜200 ng/μl by determining the absorbance at 260 nm using a Nanodrop spectrophotometer (Thermo Fisher Scientific). DNA was stored at 4° C. until future use.

A 3′-dA overhang was added to the purified blunt-end barcode cassette with an a 3′->5′ exonuclease deficient Klenow Fragment of E. coli DNA Polymerase I (New England Biolabs). Linear, end-repaired library DNA from above was heated for 3 minutes at 60° C., then immediately transferred to wet ice to cool. A 100 μl 3′-dA tailing reaction was prepared by mixing the following in a 0.2 ml PCR tube:

50 μl of end-repaired chewed-back library (˜200 ng/μl)

10 μl of 10x NEB Buffer 2

32 μl of dH₂O

2 μl of 10 mM dTTP

6 μl of Klenow Fragment (exo-) (5 U/μl).

The 100 μl reaction was incubated for 1 h at 37° C. in a thermocycler (Bio-Rad) with a block temperature set to 37° C. and a heated lid temperature of 50° C. After the 1 h incubation, the enzyme was heat-inactivated by incubation at 70° C. for 20 minutes. The reaction was allowed to cool, and then 10 μl of 10x Antarctic Phosphatase Reaction Buffer (New England Biolabs) (1X composition: 50 mM Bis-Tris-Propane HCI, 1 mM MgCl₂, 0.1 mM ZnCl₂, pH 6.0 at 25° C.) were added to the tube and the contents mixed and pulsed down. Two p1 of Antarctic Phosphatase (5U/μl) (NEB) were added, the reaction mixed, then incubated for 1 h at 37° C. The enzyme was heat-inactivated by heating the reaction to 70° C. for 5 minutes.

Next, the 5′-dephosphorylated, >8 kbp 3′-dA tailed vector was purified from <8 kbp pieces of DNA (including the excised transposon cassette) by gel purification. Twenty μl of 6X Gel Loading Dye, Blue (New England Biolabs) (1X composition: 2.5% (m/v) Ficoll-400, 11 mM EDTA, 3.3 mM Tris-HCI, 0.017% (m/v) SDS, 0.015% (m/v) bromophenol blue, pH 8.0 at 25° C.) were added to 100 μl of 5′-dephosphorylated, 3′-dA tailed vector, and 12 μl of the mixture loaded in 10 wells of a 0.8% low melting point agarose/TAE gel (Lonza SeaPlaque GTG agarose) and run alongside a DNA ladder (Quick Load 1 kb extend ladder, NEB). The gel was run at 85 V for 90 minutes, until the bromophenol blue bands migrated to the middle of the gel, then stained for 30 minutes with SYBR Safe (gel stained for 20 minutes at 25° C. with SYBR Safe (Thermo Fisher Scientific) diluted to lx concentration in TAE.

DNA bands were visualized by placing the gel atop a blue light transilluminator (Lonza) and viewing the illuminated gel through UVEX S0360X blue light blocking safety glasses (Honeywell). Gel slices corresponding to fragments of size between ˜8-15 kbp were excised with a clean single-edge safety razor blade and transferred to tared microcentrifuge tubes. DNA was recovered by adding 0.1 gel volumes of 10X β-agarase I reaction buffer (New England Biolabs), melting gel slices briefly at 65° C., cooling to 42° C., and immediately adding 1 U of β-agarase I per 100 μl of molten gel (New England Biolabs). The mixture was incubated at 42° C. for 60 min to release DNA bound in the agarose matrix. DNA was precipitated from the digested fraction of the agarase reaction by adding 0.1 volumes of 3 M sodium acetate, pH 5.4, and 2 reaction volumes of 2-propanol. After mixing, the reaction was spun at 20000xg for 15 minutes at 25° C., and the supernatant aspirated. The DNA pellet was washed twice with 900 μl of 70% ethanol, allowed to air dry briefly, then dissolved in 40 μl of (10 mM Tris-Cl, pH 8.0; 0.1 mM EDTA, pH 8.0), and allowed to solubilize overnight at 4 C. The concentration of vector DNA was found to be ˜150 ng/μl by determining the absorbance at 260 nm using a Nanodrop spectrophotometer (Thermo Fisher Scientific). A similar concentration (145 ng/μl) was determined by a fluorometric assay (Quant-iT™ PicoGreen® dsDNA Assay Kit from Thermo Fisher Scientific).

Blunt-end, 5′-phosphorylated, 60-bp barcode cassettes were prepared by PCR from ssDNA template. Oligonucleotides oBC20v1-F (5′-/5Phos/CCGTCCATGAAGGGTTCGAT-3′) (SEQ ID NO: 7) and oBC20v1-R (5′-/5Phos/ACGAATCTGCCGTTGCCATA-3′) (SEQ ID NO: 8) were ordered with covalent 5′-phosphorylation modification and standard desalting purification from Integrated DNA Technologies. Oligonucleotide pool oBC20v1-T (5′-CCGTCCATGAAGGGTTCGATNNNNNNNNNNNNNNNNNNNNTATGGCAACGGCAGATTCG T-3′) (SEQ ID NO: 9), where N indicates (A,C,G,T) was ordered with machine-mixed bases and standard desalting purification from Integrated DNA Technologies.

Two aliquots of 1.1 ml of a PCR master mix was prepared by mixing the following at bench temperature (24° C.) in two DNA LoBind Tubes (Eppendorf):

550 μl of 2x Q5 HotStart HiFi Master Mix (New England Biolabs)

385 μl of dH₂O

27.5 μl of 20 μM oBC20v1-F (fwd oligo)

27.5 μl of 20 μM oBC20v1-R (rev oligo)

110.0 of 100 nM oBC20v1-T (template)

The 2×1.1 ml PCR master mixes were briefly mixed, then distributed as 40×50 μl aliquots in 0.2 ml PCR tubes. PCR was performed using the following program in a thermocycler with heated lid (105° C.):

1 cycle of 98° C. for 30 s

5 cycles of

-   -   98° C. for 10 s     -   65° C. for 75 s

1 cycle of 65° C. for 300 s

HOLD at 10° C.

Post-thermocycling, the 40×50 μl PCR reactions were pooled and the barcode cassette purified across ten DCC-5 columns using a DNA Clean and Concentrator 5 kit (Zymo Research) per the manufacturer's instructions. DNA was eluted from each of the ten silica DCC-5 columns with 15 μl of (TE 10/0.1, pH 8.0) and the five eluted fractions pooled to obtain ˜150 μl of purified blunt-end barcode cassette. The concentration of blunt-end barcode cassette DNA was determined to be found to be ˜26 ng/μl by a fluorimetric assay (Quant-iT™ PicoGreen® dsDNA Assay Kit from Thermo Fisher Scientific). The blunt-end barcode cassette was stored at −80° C. in a DNA LoBind tube (Eppendorf) for future use.

A 3′-dT overhang was added to the purified blunt-end barcode cassette with an a 3′->5′ exonuclease deficient Klenow Fragment of E. coli DNA Polymerase I (New England Biolabs). A 300 μl reaction was prepared by mixing the following in a DNA LoBind tube (Eppendorf):

100 μl of blunt-end purified 60-bp barcode cassette (26 ng/μl)

30 μl of 10x NEB Buffer 2

146 μl of dH₂O

6 μl of 10 mM dTTP

18 μl of Klenow Fragment (exo-) (5 U/μl).

The 300 μl reaction was distributed across as 3×100 μl aliquots in 0.2 ml PCR tubes and incubated for 3 h in a thermocycler (Bio-Rad) with a block temperature set to 37° C. and a heated lid temperature of 50° C.

Post-incubation, the 3×100 μl PCR reactions were pooled and the 3′-dT barcode cassette purified with a single DCC-5 columns using a DNA Clean and Concentrator 5 kit (Zymo Research) per the manufacturer's instructions. DNA was eluted with 80 μl of (TE 10/0.1, pH 8.0). The concentration of the 3′-dT blunt-end barcode cassette DNA was determined to be found to be ˜11 ng/μl by a fluorimetric assay (PicoGreen from Thermo Fisher Scientific). The 3′-dT barcode cassette was stored in 15 μl aliquots in DNA LoBind tubes (Eppendorf) at −80° C. in a DNA LoBind tube (Eppendorf) for future use.

Next, tailed barcode cassettes were ligated into the tailed vector and the DNA circularized using a Quick Ligation Kit (New England Biolabs). A 200 μl ligation reaction was prepared in a DNA LoBind tube by combining the following:

7.0 μl of tailed vector pNL4-3 (150 ng/μl)

10.5 μl of tailed barcode (11 ng/μl)

82.5 μl of dH2O

100.0 μl of 2X Quick Ligation Buffer

10 μl of Quick Ligase (T4 DNA Ligase at 2000 U/μl)

The reaction was incubated on benchtop (24° C.) for 2 hours to perform the ligation at a 30:1 insert:vector molar ratio. The reaction was halted by adding 8 μl of (500 mM EDTA, pH 8.0) and mixing. Next, 10 μl of Proteinase K (800 U/ml) (New England Biolabs) were added, the reaction mixed, then incubated for 30 min at 37° C. to cleave bound T4 DNA Ligase from the DNA.

During the 30 minute Proteinase K treatment, 65 μl of T4 PNK (New England Biolabs) Master Mix was prepared by combining the following:

6.5 μl of 10x T4 DNA Llgase Reaction Buffer

57.5 μl of dH2O

1.0 μl of T4 PNK (10 U/μl)

After 30 minutes, the reaction was purified with 1.8 reaction volumes (360 μl) of AMPure XP beads (Beckman-Coulter) per the manufacturer's direction, and eluted from the paramagnetic beads with 65 μl of the prepared T4 DNA Ligase master mix. The eluate was incubated at 37° C. for 60 min to phosphorylate DNA at the nicked sites.

After a 60 min incubation, the nicks were sealed by treatment with Taq DNA Ligase (New England Biolabs) in 1X Taq DNA Ligase Reaction Buffer (1X composition: 20 mM Tris-HCI, 25 mM potassium acetate, 10 mM magnesium acetate, 1 mM NAD+, 10 mM DTT, 0.1% (v/v) Triton X-100, pH 7.6 at 25° C.). A 100 μl reaction was prepared by combining the following in a 0.2 ml PCR tube:

60.0 μl of T4 DNA Ligase Reaction from above

10.0 μl of 10X Taq DNA Ligase Reaction Buffer

26.0 μl of dH₂O

4.0 μl of Taq DNA Ligase (40 U/μl)

The reaction was then introduced into a thermocycler (Bio-Rad) with block temperature of 50° C. and lid temperature of 75° C. for 15 minutes to seal nicks. Ligated DNA was purified from the ligations with 1.8 reaction volumes (180 μl) of AMPure XP beads per the manufacturer's instructions (Beckman Coulter Genomics), and eluted with 42 μl of TE 10/0.1, pH 8.0. The DNA was stored at 4° C. until use.

15 μl of the 40 μl of purified ligation (˜30%) was electroporated into DH1OB E. coli, in 15 separate transformation reactions. In each transformation, 1 μl of the library was added to 40 μl of ice-cold electrocompetent E. coli (strain DH10B), and introduced into a chilled 0.1-cm sterile cuvette (Bio-Rad) placed on wet ice. Bacteria were electroporated with a Gene Pulser II electroporation system (Bio-Rad) with pulse settings of 1.7 kV, 25 μF, 200 Ω(time constant ˜5 msec). Immediately post-electroporation, 960 μl of SOC (Thermo Fisher) were added and the cell mixture transferred to a sterile 15 ml polypropylene conical tube, and allowed to recover for 90 minutes at 30° C.

After a 90 min recovery, the 15×1.0 ml recovered transformations were pooled and mixed. One hundred microliters of the 15 ml pool was added to 900 μl of SOB, vortexed to mix, then 100 μl of this dilution (corresponding to 1/1500 of the library pool) plated on each of 6×10-cm plates of containing solid media comprised of LB-Miller supplemented with 1% agar and 100 μg/ml carbenicillin (LBMA+Carb₁₀₀). The remaining 14.9 ml of the transformation was used to inoculate 500 ml of SOB+Carb₁₀₀ in a 2.8 L Fernbach flask and grown at 30° C. in a shaking incubator at 250 rpm for 24 h, until an OD600 of 3.0-4.0 was reached. The culture was chilled on wet ice and 450 ml of the 500 ml culture were harvested by centrifugation and used to prepare dry bacterial pellets for plasmid DNA isolation. The remaining 50 ml was spun down and resuspended in 14 ml of LB-Miller. To this 14 ml volume, 1.05 ml of pure DMSO (Corning) was added to adjust the concentration to 7% (v/v) DMSO. This solution was aliquoted to 15 sterile cryovials (Corning) and stored at −80° C. as seed stocks for the future library preparations.

The six plates had CFU counts of {69, 68, 73, 63, 79, 71}, avg of 70.5, which led to estimate of plated library size as 106,000 CFU (70.5×1500).

Sequencing of Plasmid Libraries

NGS libraries were prepared for paired-end sequencing on the Illumina HiSeq/MiSeq platforms. Separate sequencing libraries were prepared with a Nextera XT Kit (Illumina) from 1 ng of pNL4-3 insertion library and 1 ng of pNL4-3Δ₁ deletion library. Transposon insertion and PCR enrichment were performed per the manufacturer's instructions, but the sublibraries were pooled and size-selected by running out on a 1.5% agarose gel, staining with 1X SYBR Safe (Thermo Fisher), and excising a gel fragment corresponding to DNA of size range of 350-500 bp. DNA was purified from the gel slice using Qiagen Buffer QG, Buffer PE (Qiagen), and DCC-5 columns (Zymo Research). The sublibraries were pooled and sequenced on a single lane of a HiSeq4000 (Illumina), using 2×125 b reads at the Center for Advanced Technology at University of California, San Francisco.

Transposon insertion locations were computed by filtering for reads containing an exact match of either mosaic end sequence of TN5MK, then extracting flanking regions to build an insertion map.

A lookup table matching deletion loci to barcode sequence was determined by 1) searching reads for the forward (oBC20v1-F (5′-CCGTCCATGAAGGGTTCGAT-3′) (SEQ ID NO: 10)) and reverse (oBC20v1-R (5′-ACGAATCTGCCGTTGCCATA-3′) (SEQ ID NO: 11)) common barcode sequences and extracting the intermediate 20 b; 2) assembling a list of barcode sequences; and 3) assigning flanking regions to each barcoded deletion using custom Python software.

High MOI Passage and Sequencing of an HIV-1 Deletion Library

Virus pool was obtained by co-transfection of HEK 293T with pNL4-3 (WT virus) and the pNL4-3 deletion library. On the day of transfection, a suspension of 293T was obtained by trypsinization of subconfluent 15-cm plates of 293T and brought into single cell suspension by gentle passage through a 40 μm mesh filter (Corning). A cell count was obtained with an automated cell counter (Moxi, ORFLO), and cells were diluted to a concentration of 5E5/ml in DMEM+10% FBS. Thirty-six ml of this culture (1.8E7 cells) was added to 3 x T175 flasks. Next, 18 μg of pNL4-3, 18 μg of pNL4-3Δ₁, and 108 μl of 1 μg/μl PEI were added to serum-free DMEM supplemented with 25 mM HEPES and the volume brought to 3.6 ml with extra serum-free DMEM w/25 mM HEPES, incubated for 15 minutes, then added to the upright flasks. The upright flasks were gently rocked, then lowered to a horizontal position in a 37 C/ 5% CO2 incubator. Media was replaced after an overnight incubation (16-20 h), and virus was harvested at 40-48 hours post-transfection by passing through 0.45 μm sterile filters (Millipore). Virus stocks were concentrated by ultracentrifugation. Twenty-five ml of clarified supernatant were underlaid with a 6% (m/v) iodixanol in DPBS-CMF in SW28 ultracentrifuge tubes, and then adjusted to 38.6 ml final volume with additional clarified supernatant. The tubes were spun for 90 min at 20000 rpm in an SW28 rotor at 4 C. Supernatant was decanted and the invisible viral pellets resuspended in pure heat-inactivated FBS and frozen at −80 C.

The virus pool was cultivated by high-MOI passage on MT-4, an HIV-permissive human T cell line. On day −1, virus stocks were titrated on 2E6 MT-4 in 6-well plates and cells were stained for intracellular p24 production at 24 hours post infection with a PE-labelled monoclonal antibody (KC57-RD1, BD). On day 0 (0 hours post infection (hpi)), 2E6 MT-4 were infected at an MOI of 5-20 with the virus pool containing WT HIV-1 and tagged HIV-1 deletion mutants for 4 hours in a volume of 2 ml, then transferred to a T25 flask containing 10 ml of MT-4 at a concentration of 1E6/ml. On day 2 (40 hpi), the 12 ml of culture was transferred to a T175 containing 60 ml of MT-4 at a concentration of 1 E6/ml. On day 3 (70-72 hpi), supernatant from the MT-4 was clarified by centrifugation and 0.45 μm filtration, and then concentrated by ultracentrifugation as described above. This cycle corresponds to 3 rounds of HIV-1 replication (completed on day 1, day 2, day 3). The cycle was repeated a total of four times (12 passages / rounds of replication) to select for deletion mutants that could be efficiently mobilized by HIV-1 in high MOI passage and retained all necessary cis-acting elements. The passage scheme was conducted with 3 biological replicates.

Viral RNA was isolated from frozen aliquots of the concentrated virus pool at various time points (passage 0, passage 3, passage 6, passage 9, passage 12) using a QIAmp Viral RNA Mini Kit (Qiagen) per the manufacturer's instructions with two exceptions: 1) carrier RNA was replaced with 5 μg of linear polyacrylamide (Sigma) per isolation 2) 5E6 copies of bacteriophage MS2 RNA (Roche) were spiked in per isolation.

Purified RNA was reverse-transcribed with Superscript III (Thermo Fisher) and Random Primer Mix (New England Biolabs). cDNA was used as template in real-time qPCR to quantitate barcode cassette concentrations with oligonucleotides oBC20v1-F (5′-/5Phos/CCGTCCATGAAGGGTTCGAT-3′) (SEQ ID NO: 12) and oBC20v1-R (5′-/5Phos/ACGAATCTGCCGTTGCCATA-3′) (SEQ ID NO: 13), and compared to a standard curve prepared with dilutions of a barcode standard, oBC20v1-T (5′-CCGTCCATGAAGGGTTCGATNNNNNNNNNNNNNNNNNNNNTATGGCAACGGCAGATTCG T-3′) (SEQ ID NO: 14) in 10 μl reactions with Fast SYBR® Green Master Mix (Thermo Fisher). vRNA samples were not DNasel-treated before reverse transcription, but DNA levels were acceptably low (-RT controls had barcode levels of <1/1000x of +RT reactions).

Illumina sequencing libraries were prepared by a modification of a method specified in Mandell2015 (Mandell et al, 2015 (doi:10.1038/nature14121)). Barcode cassettes were amplified from cDNA from above using a minimum number of cycles (typically 12-18) to prevent overamplification (post log-phase PCR) as evidenced by the RT-qPCR data from above. Illumina adaptors were added by two rounds of PCR (5 cycles each), to add phasing adaptors, random barcodes, and multiplexing barcodes. Sublibraries were size-selected on 5% TBE polyacrylamide gels and pooled for sequencing.

20-30 sublibraries were sequenced on two lanes of a HiSeq4000 (Illumina) (spiked with 25% PhiX), using a single 1×50 b reads at the Center for Advanced Technology at University of California, San Francisco.

Barcodes were tallied using custom Python software and matched to deletion loci using the lookup table prepared previously to calculate deletion depth.

Construction of Transposon Cassettes (TN5MC and TN5MK)

Transposon cassettes were ordered in 3 pieces as synthetic dsDNA (<500 bp) (gBlocks, Integrated DNA Technologies) and cloned by Gibson Assembly into pUC19 (linearized at the BamHI site). For the chloramphenicol-resistance transposon cassette (TN5MC), chloramphenicol-resistant pTN5MC transformants were selected on LB supplemented with 100 μg/ml carbenicillin and 33 μg/ml chloramphenicol at 37 C. For the kanamycin-resistance transposon cassette (TN5MK), kanamycin-resistant pTN5MK transformants were selected on LB supplemented with 100 μg/ml carbenicillin and 50 μg/ml kanamycin.

EXAMPLE 1 Construction of an Insertion Library

The starting template was a population of circular target DNAs, in this case copies of the same plasmid, where the plasmid included sequence of a wildtype viral genome (FIG. 1, FIG. 2). A target sequence for a sequence specific DNA endonuclease, in this case recognition sequences for two meganuclease restriction sites, were introduced into the starting template via in vitro transposition with a modified Tn5 transposon and hyperactive Tn5 transposase (FIGS. 3-4). The custom transposon cassette harbored a drug-selectable marker (Kan^(R) or Cm^(R)) flanked by meganuclease recognition sites I-Scel and I-Ceul (FIG. 3, FIG. 4, FIG. 20). E. coli were transformed with transposed DNA and insertion mutants were selected by plating on antibiotic-supplemented media. After recovery of the transposed DNA, the result was a population of plasmids, each containing a single transposon insertion, i.e., a population of transposon-inserted circular target DNAs. FIG. 5 depicts a plot of transposon insertion location vs genome position for transposon insertions (transposon-inserted circular target DNAs) generated using the methods disclosed herein. The data presented in this figure (obtained by deep-sequencing the transposon insertion library) show that transposons were integrated at a diversity of sites.

EXAMPLE 2 Generation of Tagged Deletion Mutants

Transposon-inserted DNA was digested with I-Scel or I-Ceul, liberating the inserted transposon cassette and generating a linearized molecular clone (FIG. 6). Deletions were performed in a one-pot reaction by treating linearized DNA with a mixture of three enzymes: T4 DNA Polymerase (a 3→45′ exonuclease without dNTPs), RecJ (a 5′→43′ exonuclease) and single-strand binding protein (SSB) (FIG. 6, FIG. 7, FIG. 8). Here, the double-end chew-back rate proceeded at a rate of 50 bp/min at 37° C. and at a reduced rate at lower temperatures (FIG. 9). Thus, modulating the duration and temperature of the chewback reaction allowed for control of deletion size.

Vector DNA ends were blunted, dephosphorylated, and modified by a single 3′-dA overhang (FIG. 6). The vector was recircularized by ligation to a 3′-dT-tailed barcode cassette drawn from a pool of random barcode cassettes (a 60 bp cassette including 20 bp random barcode flanked by 20 bp primer binding sites) (FIG. 6). The nicked hemiligation product was sealed and transformed into the host bacteria. In this way, each deletion mutant was tagged with a unique barcode cassette with high probability.

EXAMPLE 3 Sequencing to Map Barcodes to Deletion Loci

The plasmid library was fragmented and deep-sequenced (e.g., 2×125 bp reads, HiSeq4000), and the results used to link barcode (bc) sequences to deletion sites (FIG. 10). The result was a lookup table mapping the set of barcodes (B={b₁,b₂,b₃, . . . } to deletion loci (D=d₁,d₂,d₃, . . . ).

Each of the m deletion mutants is described as a sparse genotype bitvector m of dimensions (L×1), where L is the integer length of the undeleted wildtype sequence. Within the mutation bitvector m, l's indicate that a base has been deleted and 0's indicate that a base has been retained. In general, deep sequencing the barcoded libraries, allows for computation of a count c, for each mutant by measuring the number of times a particular barcode is observed. The deletion depth vector d (the deletion depth profile) has dimensions (L×1) and is computed by multiplying genotype matrix M by count vector c, yielding (d=Mc). The genotype matrix M is a (0,1)-matrix of dimension L×m, while the count vector has dimensions (m×1). The genotype matrix M describes the genotypes of the barcoded mutants, where column i is the genotype bitvector of deletion mutant i. Within the count vector c, element i describes how many times the barcode associated with mutant i was observed.

FIG. 11 shows a histogram of deletion sizes that were generated when generating an HIV-1 deletion library (pNL4-3Δ₁). As can be seen in the figure, a diverse range of different sized deletions were generated. FIG. 12 shows a plot of deletion depth that was obtained for the same library as FIG. 11. The plot demonstrates that the deletion library was comprehensive (coverage over the genome) and relatively unbiased. The valley surrounding ori/bla (required for plasmid maintenance in culture) shows that bacteria harboring plasmids with deletions in this region were select against.

EXAMPLE 4 An Unbiased Procedure to Identify Essential Viral Cis-Acting Elements

In order to function as an effective TIP, a viral mutant retains the necessary cis-acting elements required for replication when complemented by the wildtype genome. The cis-acting elements of HIV-1 were mapped by producing virus from the deletion library (by transfection of the plasmid library into 293T) and using this virus pool to infect target cells at high multiplicity of infection (MOI) (FIG. 13). Sequencing of the barcodes at critical points in the infection cycle (transcription, encapsidation, reverse transcription, integration, etc.) and referencing the barcode/deletion lookup table allowed for the identification of regions where deletions were tolerated in each step of the HIV-1 replication cycle (FIG. 14). With high MOI infection, trans factors were provided by co-infection with replication-competent virus. Therefore, genome regions that can tolerate deletions (as measured by enrichment of deletion sites) correspond to trans-acting elements while regions that are intolerant of deletion correspond to cis-acting elements (FIG. 15, FIG. 16, FIG. 17, FIG. 18).

EXAMPLE 5 Screening for TIPs by High- and Low-MOI Passage of Deletion Mutants

High multiplicity of infection (MOI) passage of viruses is a method to generate defective interfering particles/therapeutic interfering particles. Here cells are infected by more than one virus, which allows for complementation of defective viruses by wildtype counterparts.

In this case, an HIV (NL4-3) viral deletion library was generated (i.e., the target DNAs included an HIV genome), and cells were then infected at high-MOI (MOI of 5-20). Repeated passaging of the deletion mutant libraries at high-MOI selected for mutants that could be mobilized effectively by HIV-1 (FIG. 17, FIG. 18). However, in some cases a method such as this may select for TIPs which can be mobilized effectively by the wildtype virus, but are cytopathic in the absence of the wildtype coinfection.

In a more stringent screen, low-MOI infection (MOI of <1) of target cells with tagged deletion libraries and high-MOI infection (MOI≥1) of the transduced population with wildtype virus (HIV-1) is alternated to mobilize TIPs to naive cells (FIG. 19). In between successive infections, the cells can be propagated in the presence of a drug to prevent further rounds of replication (e.g., Darunavir, an HIV-1 protease inhibitor). During this recovery period, HIV-1 infected cells will be killed, but cells transduced by well-behaving mutants (which do not produce cell-killing trans-factors) will be maintained. In this fashion, mutants can be selected for which do not kill their transduced host-cell but can mobilized during wildtype virus coinfection.

In both screens, the profile of deletion loci are monitored by their deletion barcodes (lineage tracking) and the fittest strains can be isolated (or cloned, synthesized) and characterized.

EXAMPLE 6 High-MOI Screen of an HIV-1 Random-Deletion Library

This Example demonstrates how a viral pool produced from a plasmid random deletion library can be screened for cis and trans-acting elements by high-MOI passage, and how to identify deletion mutants that are not replication-competent, but can be mobilized by the wildtype virus. Thus from first principles, cis- and trans-acting elements of viruses can be identified as well as transmissible antivirals.

Materials and Methods Cell Culture Methods

293T (synonyms: HEK 239T, 293tsA1609neo) were obtained from the American Type Culture Collection (ATCC, #CRL-3216). Adherent 293T were propagated in D10 media, comprised of Dulbecco's Modified Eagle's Medium (DMEM; Corning, #10-013-CV) supplemented to a final concentration of: 10% (v/v) heat-inactivated fetal bovine serum (FBS) (Corning, #35-011-CV), 100 IU/ml penicillin & 100 μg/ml streptomycin (Corning, #35-002-CI), 25 mM HEPES (Thermo Fisher, #15630080), and 2 mM L-alanyl-L-glutamine (Corning, #25-015-CI). The cell line was cultivated in 15-cm polystyrene dishes in a humidified incubator at 37° C. with 5% CO₂. Subcultures were prepared by removing media, washing once with DPBS-CMF, treating with 0.25% Trypsin/2.21 mM EDTA in HBSS for 2-5 min at 37° C., then quenched by adding an equal volume of D10.

MT-4 cells (a CD4⁺ T cell line) were obtained through the NIH AIDS Reagent Program, (Catalog #120). Cells were propagated in R10 media, comprised of Roswell Park Memorial Institute (RPMI-1640; Corning, #10-040-CV) supplemented to a final concentration of: 10% (v/v) heat-inactivated fetal bovine serum (FBS) (Corning, #35-011-CV), 100 IU/ml penicillin & 100 μg/mI streptomycin (Corning, #35-002-CI), 10 mM HEPES (Thermo Fisher, #15630080), and 2 mM L-alanyl-L-glutamine (Corning, #25-015-CI). The cell line was cultivated in sterile polystyrene T flasks within in a humidified incubator at 37° C. with 5% CO₂. Once established, cultures were maintained a density of 2·10⁶-2·10⁷ cells per ml. Subcultures were prepared by diluting cultures with fresh R10 media to about 5·10⁶ cells/ml every 2-3 days.

Production of Viral Stocks by Transfection of 293T

A virus pool was obtained by co-transfection of 293T with pNL4-3 μlasmid (WT virus) and the pNL4-3 deletion library (pNL4-3Δ₁) plasmid pool prepared above in Examples 1 and 2. On the day of transfection, a suspension of 293T was obtained by trypsinization of subconfluent 15-cm plates of 293T and brought into single cell suspension by gentle passage through a 40 μm nylon mesh filter (Corning #352340). A cell count was obtained with an automated Coulter cell counter (Moxi, ORFLO), and cells were diluted to a concentration of 5·10⁵ cells/ml in D10. Thirty-six ml of this suspension (1.8.10⁷ cells) were added to 3xT175 flasks.

Next, 18 μg of pNL4-3, 18 μg of pNL4-3Δ₁, and 108 μl of a 1 μg/μl polyethyleneimine (PEI) solution (prepared from 25 kDa linear PEI; Polysciences #23966-1) were added to serum-free DMEM supplemented with 25 mM HEPES and the volume brought to 3.6 ml with additional serum-free DMEM with 25 mM HEPES, incubated at bench temperature (24° C.) for 15 min, then added to the upright T175 flasks. The upright T175 flasks were gently rocked, then lowered to a horizontal position in a 37° C./5% CO₂ incubator. Media was replaced after an overnight incubation (range 16-20 h), and virus was harvested at 40-48 hours post-transfection by passing the virus-containing growth media through 0.45 μm sterile PVDF filters (Millipore, #SE1M003M00).

Virus stocks were concentrated by ultracentrifugation. Twenty-five ml of 0.45 μm filtered supernatant were underlaid with 5 ml of a 6% (m/v) iodixanol (Sigma #D1556) in DPBS (Calcium/Magnesium Free) solution in SW28 ultracentrifuge tubes (Beckman-Coulter #344058), then adjusted to a 38.5 ml final volume with additional 0.45 μm clarified filtrate. The tubes were spun for 90 min at 20,000 rpm in an SW28 rotor (Beckman-Coulter) at 4° C. The virus-depleted supernatant was decanted and the invisible viral pellets resuspended in pure heat-inactivated FBS and stored frozen in single-use aliquots at -80° C.

Titration of Viral Stocks

Infectious HIV-1 viral stocks were titrated by infecting cultures of MT-4 in 6-well plates with viral inocula and scoring for HIV p24-producing cells at 24 hours post-infection. HIV p24-producing cells included cells that are productively infected with wildtype HIV-1 and/or deletion mutants that are still competent to produce p24.

Briefly, 100 μl of HIV-1 inoculum was added to 1.0 ml of R10 containing 2·10⁶ MT-4, mixed briefly, then incubated for 4 hours at 37° C. After four hours, an additional 1.0 ml of R10 was added and the infection was allowed to proceed for an additional 20 hours (a single-round of replication). At 24 hours post-infection, cultures were fixed by adding 0.1 volumes of 20% formaldehyde (tousimis #1008A) (final concentration 2.0%) and incubated for at least 1 hour at 4° C. to inactive infectious virus.

Formaldehyde-fixed cells were permeabilized by treatment with 75% ice-cold methanol for 10 minutes, then stained with a phycoerythrin-labelled monoclonal antibody against HIV-1 p24 (KC57-RD1,Beckman Coulter #6604667) in a staining buffer (DPBS-CMF+2% FBS+2 mM EDTA+0.1% IGEPAL-CA630) for 30 min before washing once in stain buffer without antibody. At least 50,000 live cells were counted by flow cytometry on a FACS Calibur DxP8. Gates were drawn based upon stained naïve cell population. A representative example is shown in FIG. 25.

Values are reported as I U/ml, where an IU (infectious unit) is the amount of virus needed to produce a p24+MT-4 cell at 24 hpi. As shown in FIG. 25, titers of concentrated HIV-1 stocks averaged 5.10⁷ I U/ml.

High-MOI Passage of Virus Produced from a Random Deletion Library

A virus pool containing wildtype HIV-1 (NL4-3) and deletion mutants (NL4-3Δ₁) was prepared by co-transfection of 293T with equal masses of the pNL4-3Δ₁ library and the parental wildtype plasmid (pNL4-3) as described above. The virus-containing supernatant was collected, clarified by 0.45 μm filtration, then concentrated by ultracentrifugation at 48 hpi and titrated. The concentrated stock was used to infect MT-4 at high multiplicity of infection (>5) and passaged at high MOI (>5) as detailed below and in FIG. 26.

On day 0 (0 hpi), 2·10⁶ MT-4 were infected at an MOI of 5-20 with the virus pool containing WT HIV-1 and tagged HIV-1 deletion mutants for 4 hours in a volume of 2 ml, then transferred to a T25 flask containing 10 ml of MT-4 at a concentration of 10⁶ cells/ml. On day 2 (40 hpi), the 12 ml of culture was transferred to a T175 flask containing 60 ml of MT-4 in R10 at a concentration of 10⁶ cells/ml. On day 3 (70-72 hpi), supernatant from the MT-4 was clarified by centrifugation and 0.45 μm filtration, and then concentrated by ultracentrifugation as described above. This cycle corresponds to 3 rounds of HIV-1 replication (completed on day 1, day 2, day 3). The cycle was repeated a total of four times (12 passages/rounds of replication) to select for deletion mutants that could be efficiently mobilized by HIV-1 in high MOI passage and retained all necessary cis-acting elements. The passage scheme was conducted with 3 biological replicates. A diagram of the passage scheme is shown in FIG. 24.

Virus stocks were titrated by infecting MT-4 and scoring for cells producing HIV Gag (p24) by flow cytometry.

Values are reported as I U/ml, where an IU (infectious unit) is the amount of virus needed to produce a p24+MT-4 cell at 24 hpi. As shown in FIG. 25, titers of concentrated stocks averaged 5.10⁷ IU/ml.

Although viral stocks were of sufficient titer to provide good coverage of the library (2·10⁶ cells infected at an MOI of 5 yields 10⁷ infections), it was necessary to confirm that high MOI would be maintained in subsequent passages.

In this scheme, shown in FIG. 26, virus can be transmitted by cell-to-cell and cell-free transfer. We confirmed that high MOI could be maintained by staining samples of cells for HIV p24 production throughout the passage. A representative example shown in FIG. 27 shows that >99% of cells were p24⁺ at various points in the transfer, indicating a high-MOI passage. These passage conditions were maintained throughout the passage scheme and the p24-staining procedure was repeated during each week of passage to confirm that high MOI passage conditions were maintained. The high MOI passage conditions select for two phenotypes of virus: (a) replication-competent viruses and (b) replication-defective viruses that are efficiently trans-complemented by wildtype virus (mobilized).

Isolation of vRNA and Quantitation of WT and Deletion Mutant Levels

Viral RNA was isolated from frozen aliquots of the concentrated virus pool at various time points (passage 0, passage 3, passage 6, passage 9, passage 12) using a QIAmp Viral RNA Mini Kit (Qiagen) per the manufacturer's instructions with two exceptions: (1) carrier RNA was replaced with 5 μg of linear polyacrylamide (Sigma #56575-1ML) per isolation (2) 5·10⁶ copies of bacteriophage MS2 RNA (Roche, #10165948001) were spiked-in per isolation.

Total cellular RNA from 293T cells was isolated using Trizol (Life Technologies) from cell pellets obtained at the time of viral harvest. A poly(A) fraction, representing mRNA, was isolated by annealing total RNA to magnetic (dT)₂₅ beads to pull down polyadenylated transcripts using a commercial kit (NEBNext Poly(A) mRNA magnetic isolation module). Purified RNA was reverse-transcribed with Superscript III (Thermo Fisher) and Random Primer Mix (New England Biolabs). cDNA was used as template in real-time qPCR to quantitate barcode cassette concentrations with oligonucleotides oBC20v1-F (CCGTCCATGAAGGGTTCGAT) (SEQ ID NO:17) and oBC20v1-R (ACGAATCTGCCGTTGCCATA) (SEQ ID NO:18) and compared to a standard curve prepared with dilutions of a barcode standard, oBC20v1-T: CCGTCCATGAAGGGTTCGATNNNNNNNNNNNNNNNNNNNNTATGGCAACGGCAGATTCG T (SEQ ID NO:19), in 10 μl reactions with Fast SYBR Green Master Mix (Thermo Fisher). Levels of total HIV RNA were estimated by levels of HIV pol with oligos oNL43pol-F (GAGACAGGGCAAGAAACAGC) (SEQ ID NO:20) and oNL43pol-R (AACAGGCGGCCTTAACTGTA) (SEQ ID NO:21). Samples were normalized for recovery by determining levels of MS2 RNA recovered by oligos oMS2-F (TCCTGCTCAACTTCCTGTCGAG) (SEQ ID NO:22) and oMS2-R (CAGGTCAAACCTCCTAGGAATG) (SEQ ID NO:23) (sequences from (Vermeire, J. et al. PLoS One, 7, e50859 (2012)). Samples were not DNasel-treated before reverse transcription, but levels of background DNA were acceptably low (-RT controls had barcode levels of <1/1000x of +RT reactions).

Viral RNA was purified from concentrated viral stocks and cell pellets at various points during the high MOI passage. During purification of viral RNA, 5·10⁶ copies of a heterologous sequence (bacteriophage MS2) were spiked in to each purification to normalize recoveries and to serve as a normalization and recovery control.

Levels of barcode cassette (BC) and HIV-1 pol (POL) were determined by RT-qPCR. Genomes containing a tagged deletion will harbor BC and genomes that retain the wildtype pol sequence (all wildtype HIV and mutants that do not have a deletion in pol). Thus BC signal correlates with the concentration of tagged deletion mutants and POL as a measure of total viral genome concentration (provided that pol deletion mutants are in the minority). RT-qPCR data for supernatant concentrations are listed in Table 1 as quantification cycle (C_(q)) values. Higher values of C_(q) indicate reduced abundance of a template molecule; lower values of C_(q) indicate increase abundance and the scale is logarithmic in base 2, with a ΔC_(q) of 1 corresponding to an ≈2-fold difference and a ΔC_(q) of 3 corresponding to an ≈8-fold difference. Importantly, the BC primers form a stable primer dimer structure that is amplified even without the presence of template (no-template controls: NTC reactions). The limit of detection for BC is somewhere in the interval of C_(q) 29-35. True primer dimers and true barcode samples can be differentiated by a melt-curve after cycle 40 of qPCR.

Results

The results of the RT-qPCR analysis are provided in Table 1 below.

TABLE 1 sample Flask(s) Δ lib. barcode HIV_pol MS2 293T ABC − 34.8 ± 2.2 13.9 ± 0.6 30.8 ± 0.2 293T KLM + 16.9 ± 0.2 13.1 ± 0.3 29.1 ± 0.8 passage 3 C − 34.8 ± 0.1 11.0 ± 0.1 29.6 ± 0.3 passage 3 K + 16.8 ± 0.2 11.9 ± 0.1 30.7 ± 0.3 passage 3 L + 15.8 ± 0.8 11.5 ± 0.1 30.7 ± 0.2 passage 3 M + 16.5 ± 0.2 11.2 ± 0.1 30.6 ± 0.1 passage 6 C − 34.7 ± 0.3 11.7 ± 0.1 30.3 ± 0.2 passage 6 K + 16.7 ± 0.4 10.9 ± 0.1 29.7 ± 0.4 passage 6 L + 17.7 ± 0.2 11.8 ± 0.1 30.1 ± 0.4 passage 6 M + 17.5 ± 0.3 12.1 ± 0.1 30.3 ± 0.1 passage 9 C − 35.2 ± 0.8 12.0 ± 0.1 29.1 ± 0.4 passage 9 K + 17.7 ± 0.1 11.4 ± 0.1 29.5 ± 0.2 passage 9 L + 18.1 ± 0.2 11.9 ± 0.1 29.5 ± 0.2 passage 9 M + 17.7 ± 0.1 11.5 ± 0.1 29.8 ± 0.1 passage 12 C − 35.3 ± 0.3 13.6 ± 0.1 32.7 ± 0.2 passage 12 K + 18.6 ± 0.2 11.4 ± 0.3 30.6 ± 0.1 passage 12 L + 17.3 ± 0.2 10.1 ± 0.1 29.7 ± 0.4 passage 12 M + 17.6 ± 0.1 10.6 ± 0.1 30.0 ± 0.4 Media only − >40 37 ± 1 30.6 ± 0.9 80 ng MS2 RNA − 39.6 ± 0.2 35.2 ± 0.6 11.6 ± 0.1 NTC (no template >40  37 ± 2.1 36.9 ± 0.3 Ctrl) 293T pool, −RT + 24.7 ± 0.2 21.3 ± 0.2 34 ± 1 P3 pool, −RT CKLM + 29.2 ± 0.2 24.9 ± 0.1  34 ± 1.6 P6 pool, −RT CKLM + 30.1 ± 0.3 24.8 ± 0.3 35.8 ± 0.9 P9 pool, −RT CKLM + 31.2 ± 0.1 25.1 ± 0.4 35.6 ± 0.3 P12 pool, −RT CKLM + 31.2 ± 0.5 24.3 ± 0.1 35.9 ± 0.3

HIV pol was detected in the cultures containing WT virus, but was only detectable at background levels in media obtained from uninfected MT-4 cells. BC was detectable in supernatant from cultures containing the deletion library (KLM), but only at background levels in the WT only culture (C). In samples where reverse transcriptase was not added, (-RT), levels of barcode cassette and pol were >10 C_(q) above the +RT controls, indicating that DNA contamination was negligible (RNA predominates by ≈1000× over cDNA). Without intending to be bound by any particular theory, the source of DNA is likely cell fragments and membrane blebs from dying cells. Contamination may also be due to reverse transcription products from intravirion reverse transcription, a phenomenon observed in retroviruses. As levels of DNA were low compared to RNA, additional DNAsel treatment was not performed before downstream processing.

Throughout the passage, levels of BC and POL remained relatively constant from passage to passage and between the three triplicate flasks (K/L/M). Thus the barcoded deletion mutants were stably maintained. No differences in total HIV copy number from flasks with and without the NL4-3Δ₁ library were observed, indicating no significant amounts of aggregated interference from mutants lacking pol.

Intracellular RNA was also isolated from 293T cells that were transfected with pNL4-3 (WT HIV) and the pNL4-3Δ₁ deletion library and RT-qPCR was performed. Total RNA was isolated with TRI-Reagent, and a poly(A) fraction was obtained by annealing to paramagnetic poly-dT beads. The total RNA fraction contained a considerable amount of DNA (from transfection plasmids), but the poly(A) fractionation effectively removed most of this. The poly(A) fraction corresponds to poly(A) mRNA, which requires complete transcription. RT-qPCR results are listed in Table 2. As with the supernatant data in Table 1, BC was only detected when the deletion library was included, and BC and POL were not detectable in naïve 293T cells.

TABLE 2 HIV-1 qPCR data (transfection, intracellular) sample Flask(s) WT Δ barcode HIV_pol MS2 total naïve − − 34.6 ± 0.7 29.9 ± 0.1 36.9 ± 0.2 total ABC + − 34.6 ± 0.4 13.6 ± 0.1 37.6 ± 0.7 total KLM + + 17.2 ± 0.3 14.0 ± 0.1 37.2 ± 0.2 poly(A) naïve − − 33.6 ± 0.7 28.9 ± 0.4 35.7 ± 0.4 poly(A) ABC + − 34.3 ± 0.5 14.9 ± 0.1 35.8 ± 0.2 poly(A) KLM + + 18.1 ± 0.1 15.6 ± 0.2 37.2 ± 0.7 total pooled, -RT + + 23.6 ± 0.5 19.8 ± 0.2 36.7 ± 0.6 poly(A) pooled, -RT + + 30.4 ± 0.3 32.3 ± 0.9 36.0 ± 0.1 MS2 N/A − − 36.1 ± 1.4 36.5 ± 0.5 28.4 ± 0.2 NTC N/A − − >40 34 ± 5 37.0 ± 0.8

EXAMPLE 7 Preparation and Analysis of Barcode Data

This Example details a method of preparing sequencing libraries of barcode sequences and identifying cis- and trans-acting regions of viruses.

In order to function as an effective TIP, a viral mutant must retain all necessary cis-acting elements required for replication so that it may be complemented by the wildtype virus. In this example, the cis and trans-acting elements of HIV-1 are identified by genetic screen by serial, high-MOI passage of NL4-3 and the NL4-3Δ₁ deletion library prepared as described above.

In a high MOI infection, trans factors are provided by co-infection with replication-competent virus. Therefore, genome regions that can tolerate deletion (as measured by enrichment of specific barcodes) correspond to trans-acting elements while regions that are intolerant of deletion correspond to cis-acting elements. By passaging random deletion libraries of a virus under high MOI conditions, a practitioner can functionally characterize the collection of diverse deletion mutants in order to map cis-acting elements of HIV-1. Viral mutants which persist through multiple passages are either (a) replication-competent or (b) able to be trans-complemented by the wildtype virus.

Two technical considerations should be considered when planning the experiment. To achieve efficient trans-complementation, cells should be infected at a high MOI, so that on average, each cell is infected with more than one virus, and preferably at least one copy of the wildtype virus to supply trans factors. For MOI >5, the majority of cells should receive at least one copy of the wildtype genome to supply the missing trans factors.

For the second consideration, undersampling of the library can prevent acquisition of meaningful data from the experiment. Thus, to keep strong selective pressure and to avoid drift, the diversity of the library should be limited to be fewer than the number of infected cells, so that most of the library will be sampled multiple times during infection.

In this example, the passaging was performed with 3 biological replicates (flasks K, L, M) that were seeded from a common pool of virus. Thus, mutants which are reliably enriched in all three flasks can be identified as retaining all cis-acting elements with high confidence. A parallel control was also developed, where only the wildtype virus would be introduced (flasks A, B, C). In this wildtype only arm (flasks A,B,C), no tagged deletion mutants (barcode cassette) are expected to be observed. The experiment is diagrammed in FIG. 24.

Materials and Methods Preparation of Barcode Sequencing Libraries

Illumina sequencing libraries were prepared by a method as detailed in FIG. 23. Barcode cassettes were amplified from cDNA from above using a minimum number of cycles (typically 12-18) to prevent overamplification (post log-phase PCR) as evidenced by the RT-qPCR data from above. Illumina adaptors were added by two rounds of PCR (5 cycles each), to add phasing adaptors, random barcodes, and multiplexing barcodes. Sublibraries were size-selected on 5% TBE polyacrylamide gels and pooled for sequencing.

20-30 sublibraries were sequenced on two lanes of a HiSeq4000 (Illumina) (spiked with 25% PhiX), using a single 1×50 b reads.

Barcodes were tallied using custom Python software and matched to deletion loci using the lookup table prepared previously to calculate deletion depth.

Robustness of Barcode Passage

Using the C_(q) values of barcode cassettes measured by RT-qPCR in Example 6 (cf. Tables 1 and 2), Illumina sequencing libraries were prepared to characterize which barcodes were persisted throughout the high MOI passage. Barcode cassettes were amplified exponentially for a minimum number of cycles, and then multiplexing indices and Illumina TruSeq adapters were added by two additional rounds of PCR. From RT-qPCR, it was established that the number of template molecules for each PCR reaction was >10⁷. Using the barcode-to-deletion mapping for the 23,851 mappable mutants in pNL4-3Δ₁, the count of each barcode cassette (with a known deletion locus), was tabulated, and used to compute the prevalence, f_(t) of each barcode cassette i in each sample.

Identification of Cis-Acting Elements through High MOI Passage

The pool of NL4-3Δ₁ deletion mutants was passaged 12 times at high multiplicity-of-infection (MOI) in a permissive T-cell line, MT-4. Samples were collected every 3 passages and deletion depth profiles built by deep sequencing of the barcoded deletion mutants.

Results

Robustness of Barcode Passage

Pairwise correlation plots of all barcodes in triplicate flasks (K,L,M) at passage 3 and passage 12 are plotted in FIG. 28. Coefficients of determination (R²) at early timepoints (passage 3) were on average greater than at passage 12 (R²≅0.93) and at later timepoints dipped slightly to (R²≅0.83). Thus, there was strong concordance between the triplicate infections at each stage of passage scheme. Thus, the selection scheme is robust. Knowledge that a particular barcode is enriched in one replicate provides confidence that the same barcode will be reliably enriched in the other replicate flasks. For most barcodes, knowledge of barcode prevalence in one flask is predictive of the prevalence in other flasks.

Identification of Deleterious and Adaptive Mutations

During high MOI passage, two phenotypes of deletion mutants that persist throughout passage are selected. Persistent mutants are either replication-competent (are self-mobilized) or are replication-defective but can be efficiently trans-complemented by the wildtype virus.

Using deep sequencing, the prevalence of each mutant in the total population of barcoded mutants was tabulated, and c prevalence trajectories computed throughout the passage. If a particular mutation becomes more prevalent over time, it is adaptive: it confers a fitness advantage (fitness is greater than average fitness at that point). If a particular mutant or mutation becomes less prevalent, then the mutation is deleterious (fitness decrease relative to average fitness). If prevalence remains constant, then the mutation is neutral. Once a mutant falls below a prevalence of 1/N where N is the population size (10⁵ to 10⁶ in this experiment), it is likely to be lost due to drift . This corresponds to log₁₀(prevalence) of −5.0 to −6.0.

Of the 23,851 mappable NL4-3 deletion mutants, only 4390 (18%) were extant in all three replicate flasks by passage 12—the remaining 19,461 (82%) were extinct in at least one of the three replicates.

Prevalence trajectories were computed for these 4390 extant mutations and the slope in prevalence was calculated versus passage number by linear regression, as shown in FIG. 29. After fitting linear regression lines to these 4390 mutants, it was observed that 1390 (32%) increased in prevalence through every passage, indicating that deletion mutants harboring these deletions were transmitting better than the average member of the barcoded population (FIG. 30). The remaining 3000 mutants remained steady or decreased in prevalence through every passage. As barcode levels were relative constant in comparison to total HIV POL (as shown previously in RT-qPCR data), it is clear that these 1390 deletions mutants were transmissible and could spread through the population as fast or faster than the wildtype virus. Thus, these 1390 deletions represent a potential collection of deletion mutants that are transmissible (R₀>1) under these conditions of high MOI passage in MT-4 as they are expanding in the population.

Identification of Cis-Acting and Trans-Acting Elements

Using deep sequencing counts of each barcode cassette (vector c) and the barcode-to-genotype mapping prepared in Example 3 (genotype matrix M), a deletion depth profile for the HIV-1 genome at each timepoint using the formula (d=Mc, described in Example 3) was computed. Regions where the deletion depth is large correspond to genomic intervals that are tolerant to deletion (trans-acting elements encoding common goods). Intervals where the deletion depth is low or tends to 0 correspond to cis-acting elements, and cannot be complemented in trans. Deletion depth is presented in terms of raw units (unnormalized), and depends on the sequencing depth of each library.

As a baseline, the deletion depth profile of the pNL4-3Δ₁ deletion library across the pNL4-3 provirus was computed, shown in FIG. 31.The deletion depth across the genome is nonzero and flat across 0-4 kbp before rising to a peak centered at the N-terminus of env, and falling towards the 3′ end of the genome. Bias in deletion depth at this stage corresponds to differences in growth rate in the E. coli host harboring each plasmid. Faster growing bacteria will cause their harbored plasmid to be overrepresented in the library. The signal peptide of env and sequences at the N-terminus are known to be toxic to bacteria, therefore bacteria harboring env deletion mutant plasmids are likely to outgrow bacteria harboring plasmids that retain env.

Cis-Acting Elements Required for Transcription

The poly(A) fraction of RNA isolated from 293T co-transfected with the pNL4-3Δ₁ deletion library and pNL4-3 represents mRNA. Barcodes found in this fraction represent genomes that have been successfully transcribed from the HIV-1 provirus. Areas of low deletion depth (compared to the plasmid library profile) correspond to cis-acting elements required for transcription in 293T. A deletion depth profile for this poly(A) RNA fraction is shown in FIG. 32.

The deletion depth profile of the poly(A) fraction has the same basic profile as the plasmid deletion library with two notable differences. Deletions at the 5′ end of the genome (spanning the 5′ LTR through SL1-SL4) strongly inhibit transcription, as reflected by the low deletion depth. These regions encode the LTR promoter and regions necessary for splicing and efficient transcription (TAR loop). At the 3′ end of the genome, there is a decrease in deletion depth after the RRE, falling towards the 3′ LTR with respect to the plasmid deletion library profile in FIG. 31. cis-acting elements required for encapsidation and egress

A deletion depth profile of RNAs that were present in the virus-containing fraction of supernatant from transfected 293T was computed next. Barcodes found in this fraction have tagged viral genomes that could be transcribed, exported from the nucleus, and packaged into virions (encapsidated), and exported from the cell (egressed). As shown in FIG. 33, the deletion depth profile is strikingly different from the transcription of plasmid library profiles, and shows two key areas of low deletion depth, which correspond to cis-acting elements that are required for transcription and encapsidation. At the 5′ end of the genome, there is an area of zero deletion depth that begins at the 5′ LTR and continues through the 5′ UTR, (SL1,SL2,SL3,SL4) to the start codon of gag. This region is often referred to as LP, the lentiviral packaging element, and is present in many lentiviral vectors. Structural studies have identified this region to be a minimal packaging element.

At the 3′ end of the genome, there is a region of zero deletion depth that maps exactly to the Rev Responsive Element (RRE), a region of secondary structure that binds HIV-1 Rev to export incompletely spliced RNAs from the nucleus via the Crm1 pathway. The RRE is important for the steps of nuclear export and encapsidation, but this experiment cannot differentiate between nuclear export or encapsidation as the potential block, as nuclear/cytoplasmic fractionation of RNAs was not performed.

These two regions (5′ LTR/UTR and RRE) appear to be the only elements required for transcription and encapsidation of the viral genome - all other genome intervals can tolerate some amount of deletion. This is in contrast to literature reports of the GRPE (a region at the frameshift of gag/ pol, that is putatively necessary for genome encapsidation (Chamanian, M. et al. Cell Host & Microbe, 13, 181-92 (2013)). It is however, consistent with a model of Gag binding to ψ and the RRE of HIV-1 (Kutluay, S. B. & Bieniasz, P. D. PLoS Pathogens, 6, e1001200 (2010); Kutluay, S. B. et al. Cell 159, 1096-1109 (2014)).

Identification of Cis-Acting Elements through High MOI Passage

Deletion depth profiles at passage 3, passage 6, and passage 12 are shown in FIG. 34, FIG. 35, and FIG. 36. At passage 3, the deletion depth profile plotted in FIG. 34 diverges notably from the 293T supernatant profile (FIG. 33). There are three key differences: (1) a valley that appears with a minimum centered above the cPPT/CTS (2) a shift of the region of zero-deletion depth at the 5′ end of the genome, which now encompasses the 5′ LTR, 3′ UTR, and the first three hundred bases of gag, (3) a widening and 3′ shift of the valley situated above the RRE.

After 6 in vitro passages (FIG. 35), these features become more pronounced where each valley flattens to a deletion depth of zero. The 5′ shoulder of the peak situated above env also appears to increase in height.

After 12 high MOI in vitro passages (FIG. 36), areas of low deletion depth (indicating intolerance to deletion) have flattened and reached a deletion depth of approximately zero. This actual deletion depth is non-zero (values of 10-300), and without intending to be bound by any particular theory, could reflect cross-talk between libraries during demultiplexing on the IIlumina platform in addition to persistent mutants.

Using these data, a model for the cis- and trans-acting elements of HIV-1 was constructed in FIG. 37. Three regions of the HIV-1 genome are tolerant to deletion, indicating that they encode elements that can be complemented efficiently in trans. The deletion depth profile at passage 12 is annotated in FIG. 37.

This model shows trans-acting element “mountains” and one trans-acting “hill”, with peaks at the center of pol (trans-acting element 1: TAE1), in the accessory gene tract of HIV (vif-vpu) (TAE2), and in the 3′ end of env. The deletion depth profile in TAE1 (gag-pol) has a small shoulder and an inflection point corresponding to the start codon of pol. The deletion depth profile of TAE2 (post cPPT to pre-RRE) has a shoulder corresponding to the start codon of env. The last trans-acting element (TAE3) begins after splice acceptor 7 (SA7) which marks the second exon of tat and rev, and ends at the PPT. The last hill after TAE3 (within the U3 region of the 3′ LTR) may be an artifact due to the mechanism of HIV-1 genome replication, where the U3 region of the 3′ LTR is copied to the 5′ end of the DNA genome during reverse transcription. Thus, mutants with apparent deletions in U3 may persist

The deletion depth profile after passage 12 also contains four regions of low or zero deletion depth, indicating that these genomic regions cannot tolerate deletion and cannot be complemented efficiently in trans: these regions are putative cis-acting elements (CAE).

CAE1 is 1115 bp in length and maps to nucleotides 1-1114 of NL4-3 proviral genome. This 5′ end of genome encompasses the 5′ LTR, stem loops 1-4, and the first 325 b of gag, which maps to the Gag MA (p17). This region is included in lentiviral vectors and a minimal packaging element, ψ, has been mapped to this region. Why deletions in Gag MA are not tolerated remains unknown, although others have speculated that there is a relationship between encapsidation and translation of the HIV-1 genome.

CAE2 is 126 bp in length and maps to nucleotides 4779-4905 of NL4-3, at the 3′ end of env. This region maps exactly to the cPPT/CTS, a region previously identified as being necessary for reverse-transcription and integration of HIV-1. This region is conserved in lentiviruses but not retroviruses.

CAE3 is 671 bp in length and maps to nucleotides 7710-8381 of NL4-3, at the 3′ end of env. It begins exactly at the RRE, and ends precisely at splice acceptor 7 (SA7). This splice acceptor is used for splicing of several multiply spliced HIV-1 transcripts, including (vpr, tat, rev, net). This region, too, is included in many lentiviral vectors.

CAE4 is 684 bp in length and maps to nucleotides 9025-9709 of NL4-3. This region spans the PPT, necessary for reverse transcription in HIV-1 and the 3′ LTR.

Cis-Acting Elements of HIV-1

Example 6 and Example 7, when taken together, provide an approach to conducting a genetic screen to map the cis- and trans-acting elements of HIV-1 as well as many other viruses. In the screen, 293T cells were transfected with the NL4-3Δ₁ barcoded deletion library and wildtype NL4-3 to produce a pool of infectious virus. The virus pool was then passaged 12 times at high MOI (5-20) in a T-cell line (MT-4).

During high MOI infection, target cells are infected with more than one virus with high probability, allowing replication-defective viruses that retain all necessary cis-acting elements to persist through the passage by trans-complementation with common goods produced by functional wildtype virus. Thus, this screen selects two viral phenotypes: (a) replication-competent viruses (b) replication-defective viruses that retain all necessary cis-acting elements and can be mobilized effectively by wildtype HIV-1.

Sequencing of the barcodes at critical points in the infection cycle (transcription, encapsidation/egress, passage 3, passage 6, passage 12) and referencing the barcode/deletion lookup table allowed for the identification of genomic regions where deletions were tolerated in each step of the HIV-1 replication cycle (trans-acting elements) or were intolerant to deletion (cis-acting elements).

Using the high-resolution deletion depth profiles, four distinct cis-acting elements were identified, regions that that could not be complemented in trans. These regions are annotated in FIG. 37 : CAE1: nt 1-1144 of NL4-3, spanning the 5′ LTR, stem loops 1-4, and the first 325 b of gag; CAE2: nt 4779-4905 of NL4-3, the cPPT/CTS; CAE3: nt 7710-8381 of NL4-3, which begins exactly at the RRE and ends precisely at splice acceptor 7 (SA7); CAE4: nt 9025-9709 of NL4-3, which covers the PPT and the 3′ LTR.

Based upon these results, a minimal HIV-1 therapeutic interfering particle (in proviral form) might be obtained by concatenation of the sequences of CAE1 (1115 bp), CAE2 (126 bp), CAE3 (671 bp), and CAE4 (684 bp), which sum to a total length of 2596 bp. This assumes that the regions can act independently and the multiple deletions do not demonstrate epistasis.

Despite previous claims that the GRPE is important for encapsidation (Chamanian, M. et al. Cell Host & Microbe, 13, 181-92 (2013)) we show that deletions of this region do not affect mobilization, in agreement with Nikolaitchik and Hu (Nikolaitchik, O. A. & Hu, W.-S. J. Virology 88, 4040-4046 (2014)).

The screen was conducted using a single molecular clone of HIV-1 and a single clonal cell line. It is possible that cis-acting elements can vary between viral strains and between cell lines and tissue types.

Recombination between viruses was unmonitored, although it is known to be an important aspect for HIV-1 replication. Recombination can produce viral strains that have acquired more than one deletion, and create linkage effects. Additional sequencing outside of the barcode cassette region was not performed and the appearance of additional mutations was not examined. However, the dot plots in FIG. 28, show strong correlation between replicates, showing that the observed selection was deterministic, not in the region of drift.

EXAMPLE 8 Low-MOI Screen of an HIV-1 Random Deletion Library (Prophetic)

In a more stringent screen, the HIV-1 deletion library, pNL4-3Δ₁, could be passaged in permissive cells at low MOI (MOI of <1), instead of high MOI as performed in this chapter. An example scheme is depicted in FIG. 38.

Target cells are transduced/infected at low MOI with a pool of virus containing tagged deletion mutants and wildtype helper virus, and then allowed to recover in the presence of a drug (or neutralizing antibody) to restrict viral replication to a single round. During the recovery period, cells infected with wildtype virus or cytopathic deletion mutants will be killed, while uninfected cells and cells infected with non-cytopathic deletion mutants will survive. After the recovery period, the population of cells is infected at high MOI with the wildtype virus to mobilize deletion mutants. In this fashion, deletion mutants which do not kill their host cell but also retain all cis-acting elements required for transmission can be selected.

The low MOI screen is more stringent than a high MOI screen performed above, as it selects for mutants that are non-cytopathic but can be mobilized. The high MOI screen selects for mutants that are replication-competent or can be mobilized by the wildtype virus, but does not select for or against cell killing. Successive passages (every 24 hours), are performed before cell death occurs in HIV-1 infections, typically 24-72 hours post-infection (Perelson, A. S. & Nelson, P. W. SIAM Review, 41, 3-44 (1999).

EXAMPLE 9 Construction and Evaluation of Prototype DIPs for HIV-1

This Example describes how viral strains harboring multiple adaptive deletions can be recovered from data obtained during a high-MOI or low-MOI screen of a random deletion library.

An ideal transmissible antiviral (a DIP/TIP) would possess the following qualities: (1) it would compete effectively for common goods provided by the wildtype helper virus during co-infection (interference) (2) it would be retain all necessary cis-acting elements required for efficient mobilization by the helper virus (mobilization, R₀>1), (3) it would be unable to transmit without co-infection with wildtype helper virus (no self-replication).

The results of the high MOI passage screen for HIV-1 cis-acting elements in Examples 6 and 7 can be used to develop transmissible antivirals against HIV-1. From the deletion depth profile, we were able to identify four cis-acting elements that were intolerant of deletion and could not be complemented in trans. Therefore, any HIV-1 potential transmissible antiviral must retain these regions in its genome. Concatenation of these four cis-acting elements provides the minimum proviral size of an HIV-1 transmissible antiviral, about 2.6 kbp.

The high MOI passage of the pNL4-3Δ₁ deletion library also allowed an estimation of the fitness effect of each deletion (see FIG. 29 and FIG. 30). While most of the 23,851 deletions were deleterious (about 95%), 1390 mutants consistently increased in prevalence within the barcoded pool, suggesting these mutations had an adaptive effect (increase in R₀). A subset of the adaptive mutations increased in prevalence by as much as 1-2 logo over 12 passages.

By generating viral mutants harboring one or multiple adaptive deletions, as identified in the high MOI screen, it may be possible to assemble a library of potential TIPs. Such viruses can be further optimized by point mutations and further deletion.

In this Example, a collection of 60 HIV-1 subgenomic deletion mutants are reconstituted from adaptive deletions identified from the high MOI screen in Example 6 and Example 7. A subset of these satisfy the basic requirements of a transmissible antiviral in single-round replication studies: they interfere with HIV-1 replication, reducing wildtype viral loads; they can be mobilized by the wildtype helper virus to new cells, and they do not self-replicate.

Materials and Methods Cloning Strategy

The high MOI screen in Example 6 and Example 7 identified three trans-acting elements of the HIV-1 genome that were tolerant to deletion (FIG. 37). The three trans-acting elements are interleaved by four cis-acting elements that are intolerant to deletion. This genome organization can be exploited during cloning of multiply-deleted strains. As the cis-acting elements must be preserved, they can be used as fixed sequence “fasteners” to join variably-sized pieces of the trans-acting elements.

To develop a modular cloning strategy, the 9709 bp proviral genome was subdivided into 7 blocks (A, B, C, D, E, F, G) that can be joined by Gibson Assembly to create a single provirus (FIG. 39). Each block is comprised of a 400-2100 bp subsequence of pNL4-3 plasmid with flanking adapter sequences to allow assembly of full-length virus genomes by Gibson Assembly via flanking 40 bp sequences, as depicted in FIG. 39. By creating different version of blocks A through G, one can create a combinatorial library by building mutants composed of different versions of each common block to generate multiply deleted and mutated strains of HIV-1.

Using the high MOI data results, a number of deletions that were reliably enriched (4-250×) over 12 in vitro passages in all three replicates of the HIV-1 high MOI passage experiment were selected for cloning (FIG. 40 and FIG. 41). Additionally, each of the four cis-acting elements is encoded by a single block (see FIG. 39 and FIG. 41). In all, 7 mutants were selected from block B, 1 mutant from block C, 4 from block D, and 1 from block F. When combined with the wildtype piece from each block, a total of 160 viruses (159 mutants and 1 wildtype virus) can be created.

Table 3 below lists the 20 single block sequences that can be joined to generate the multiply-deleted strains of HIV-1. The sequences are provided in the attached sequence listing as SEQ ID NOs: 24-43. For each sequence, Table 3 provides a description of what deletion was made (if any) in the sequence. All numbering is with respect to the 9709 bp NL4-3 HIV-1 proviral sequence.

TABLE 3 partially SEQ or fully ID name description Δ (bp) left right barcode deleted genes NO. NL43_A00 HIV-1    0 NA NA NA None 24 subsequence A, WT NL43_B00 HIV-1 NA NA NA NA None 25 subsequence B, WT NL43_B01 HIV-1 1016 1636 2651 TTGAACCCATGGCCGG gag/pol 26 subsequence ATCA (SEQ ID NO: 44) B, Δ NL43_B02 HIV-1 1361 1455 2815 TGGACCCGCCCGGACG gag/pol 27 subsequence CTCA (SEQ ID NO: 45) B, Δ NL43_B03 HIV-1 1547 1448 2994 CAGGCAGCTCAAGAAA gag/pol 28 subsequence CACG (SEQ ID NO: 46) B, Δ NL43_B04 HIV-1  908 1469 2376 TCGACAGTGTAATGTCT gag/pol 29 subsequence GCA (SEQ ID NO: 47) B, Δ NL43_B05 HIV-1  825 1484 2308 GGGGGGCGGCGATTAC gag/pol 30 subsequence TTGT (SEQ ID NO: 48) B, Δ NL43_B06 HIV-1  860 1469 2328 GAGCTGCAGGGCATGT gag/pol 31 subsequence TATA (SEQ ID NO: 49) B, Δ NL43_B07 HIV-1  796 1560 2355 GGCGACCCTCGGCCGT gag/pol 32 subsequence GGAC (SEQ ID NO: 50) B, Δ NL43_C00 HIV-1    0 NA NA NA None 33 subsequence C, WT NL43_C01 HIV-1  987 3620 4606 CAGCTTGTTCAGATGCT Pol 34 subsequence GTA (SEQ ID NO: 51) C, Δ NL43_D00 HIV-1    0 NA NA NA None 35 subsequence D, WT NL43_D01 HIV-1  986 5073 6058 TCTTGAACAGCGCGGTC vif/vpr/tat/ 36 subsequence TGT (SEQ ID NO: 52) rev D, Δ NL43_D02 HIV-1  986 5073 6058 D01 but without vif/vpr/tat/ 37 subsequence barcode rev D, Δ NL43_D03 HIV-1 1089 5071 6159 GATCGGTCGTCGCAGC vif/vpr/tat/ 38 subsequence GGTC (SEQ ID NO: 53) rev/vpu D, Δ NL43_D04 HIV-1 1211 5041 6251 TATCTGTAGCCAACATT vif/vpr/tat/ 39 subsequence CGA (SEQ ID NO: 54) rev/vpu/env D, Δ NL43_E00 HIV-1    0 NA NA NA None 40 subsequence E, WT NL43_F00 HIV-1    0 NA NA NA NA 41 subsequence F, WT NL43_F01 HIV-1  174 9116 9289 CGTAAAGTGGGATAGTT nef/U3 42 subsequence TTT (SEQ ID NO: 55) F, Δ NL43_G00 HIV-1    0 NA NA NA None 43 subsequence G, Δ

The following system is used to describe the genotype of each virus. For each block, “00” is the wildtype version, thus the wildtype version of NL4-3 can be written descriptively (yet verbosely) as NL43_A00B00C00D00E00F00G00. A mutant which is composed of mutant blocks B02, D01 and wildtype versions of the remaining blocks has the genotype of NL43_A00B02C00D01E00F01.

Using this combinatorial strategy, 61 viruses (60 deletion mutants and 1 wildtype virus) were prepared using the assembly strategy demonstrated in FIG. 39. A complete listing of the deletion mutants can be found in Tables 4 and 5 below. The hiv00 sequence corresponds to the 9709 bp NL4-3 provirus referred to herein. All numbering is done relative to this sequence. The publicly-available sequence is deposited in GenBank under accession number AF324493.2. The 9709 bp NL4-3 provirus corresponds to nt 1-9709 of this sequence.

TABLE 4 total SEQ bases deletion genes/regions partially or fully ID seq name deleted inteval(s) deleted notes NO. hiv00 NL43_A00B00C00D00E00F00G00 0 none none WT 56 hiv01 NL43_A00B00C00D00E00F01G00 174 9116- nef/U3 Δnef 57 9289 hiv02 NL43_A00B00C00D01E00F00G00 986 5073- vif/vpr/tat/rev 58 6058 hiv03 NL43_A00B00C00D01E00F01G00 1160 5073- vif/vpr/tat/rev/nef/U3 59 6058, 9116- 9289 hiv04 NL43_A00B00C00D02E00F00G00 986 5073- vif/vpr/tat/rev 6058 hiv05 NL43_A00B00C00D02E00F01G00 1160 5073- vif/vpr/tat/rev/nef/U3 61 6058, 9116- 9289 hiv06 NL43_A00B00C00D03E00F00G00 1089 5071- vif/vpr/tat/rev/vpu 62 6159 hiv07 NL43_A00B00C00D03E00F01G00 1263 5071- vif/vpr/tat/rev/vpu/nef/U3 63 6159, 9116- 9289 hiv08 NL43_A00B00C00D04E00F00G00 1211 5041- vif/vpr/tat/rev/vpu/env 64 6251 hiv09 NL43_A00B00C00D04E00F01G00 1385 5041- vif/vpr/tat/rev/vpu/env/nef/U3 65 6251, 9116- 9289 hiv10 NL43_A00B00C01D00E00F00G00 987 3620- pol 66 4606 hiv11 NL43_A00B00C01D00E00F01G00 1161 3620- pol/nef/U3 67 4606, 9116- 9289 hiv12 NL43_A00B00C01D01E00F00G00 1973 3620- pol/vif/vpr/tat/rev 68 4606, 5073- 6058 hiv13 NL43_A00B00C01D01E00F01G00 2147 3620- pol/vif/vpr/tat/rev/nef/U3 69 4606, 5073- 6058, 9116- 9289 hiv14 NL43_A00B00C01D02E00F00G00 1973 3620- pol/vif/vpr/tat/rev 70 4606, 5073- 6058 hiv15 NL43_A00B00C01D02E00F01G00 2147 3620- pol/vif/vpr/tat/rev/nef/U3 71 4606, 5073- 6058, 9116- 9289 hiv16 NL43_A00B00C01D03E00F00G00 2076 3620- pol/vif/vpr/tat/rev/vpu 72 4606, 5071- 6159 hiv17 NL43_A00B00C01D03E00F01G00 2250 3620- pol/vif/vpr/tat/rev/vpu/nef/U3 73 4606, 5071- 6159, 9116- 9289 hiv18 NL43_A00B00C01D04E00F00G00 2198 3620- pol/vif/vpr/tat/rev/vpu/env 74 4606, 5041- 6251 hiv19 NL43_A00B00C01D04E00F01G00 2372 3620- pol/vif/vpr/tat/rev/vpu/env/nef/U3 75 4606, 5041- 6251- 9116- 9289 hiv20 NL43_A00B01C00D00E00F00G00 1016 1636- gag/pol 76 2651 hiv21 NL43_A001301C00D01E00F00G00 2002 1636- gag/pol/vif/vpr/tat/rev 77 2651, 5073- 6058 hiv22 NL43_A00B01C00D04E00F00G00 2227 1636- gag/pol/vif/vpr/tat/rev/vpu/env 78 2651, 5041- 6251 hiv23 NL43_A001301C01D00E00F00G00 2003 1636- gag/pol 79 2651, 3620- 4606 hiv24 NL43_A001301C01D01E00F00G00 2989 1636- gag/pol/vif/vpr/tat/rev 80 2651, 3620- 4606, 5073- 6058 hiv25 NL43_A001301C01D04E00F00G00 3214 1636- gag/pol/vif/vpr/tat/rev/vpu/env 81 2651, 3620- 4606, 5041- 6251 hiv26 NL43_A00B02C00D00E00F00G00 1361 1455- gag/pol 82 2815 hiv27 NL43_A00B02C00D01E00F00G00 2347 1455- gag/pol/vif/vpr/tat/rev 83 2815, 5073- 6058 hiv28 NL43_A00B02C00D04E00F00G00 2572 1455- gag/pol/vif/vpr/tat/rev/vpu/env 84 2815, 5041- 6251 hiv29 NL43_A00B02C01D00E00F00G00 2348 1455- gag/pol 85 2815, 3620- 4606 hiv30 NL43_A00B02C01D01E00F00G00 3334 1455- gag/pol/vif/vpr/tat/rev 86 2815, 3620- 4606, 5073- 6058 hiv31 NL43_A00B02C01D04E00F00G00 3559 1455- gag/pol/vif/vpr/tat/rev/vpu/env 87 2815, 3620- 4606, 5041- 6251 hiv32 NL43_A00B03C00D00E00F00G00 1547 1448- gag/pol 88 2994 hiv33 NL43_A00B03C00D01E00F00G00 2533 1448- gag/pol/vif/vpr/tat/rev 89 2994, 5073- 6058 hiv34 NL43_A00B03C00D04E00F00G00 2758 1448- gag/pol/vif/vpr/tat/rev/vpu/env 90 2994, 5041- 6251 hiv35 NL43_A00B03C01D00E00F00G00 2534 1448- gag/pol 91 2994, 3620- 4606 hiv36 NL43_A00B03C01D01E00F00G00 3520 1448- gag/pol/vif/vpr/tat/rev 92 2994, 3620- 4606, 5073- 6058 hiv37 NL43_A00B03C01D04E00F00G00 3745 1448- gag/pol/vif/vpr/tat/rev/vpu/env 93 2994, 3620- 4606, 5041- 6251 hiv38 NL43_A00B04C00D00E00F00G00 908 1469- gag/pol 94 2376 hiv39 NL43_A00B04C00D01E00F00G00 1894 1469- gag/pol/vif/vpr/tat/rev 95 2376, 5073- 6058 hiv40 NL43_A00B04C00D04E00F00G00 2119 1469- gag/pol/vif/vpr/tat/rev/vpu/env 96 2376, 5041- 6251 hiv41 NL43_A00B04C01D00E00F00G00 1895 1469- gag/pol 97 2376, 3620- 4606 hiv42 NL43_A00B04C01D01E00F00G00 2881 1469- gag/pol/vif/vpr/tat/rev 98 2376, 3620- 4606, 5073- 6058 hiv43 NL43_A00B04C01D04E00F00G00 3106 1469- gag/pol/vif/vpr/tat/rev/vpu/env 99 2376, 3620- 4606, 5041- 6251 hiv44 NL43_A00B05C00D00E00F00G00 825 1484- gag/pol 100 2308 hiv45 NL43_A00B05C00D01E00F00G00 1811 1484- gag/pol/vif/vpr/tat/rev 101 2308, 5073- 6058 hiv46 NL43_A00B05C00D04E00F00G00 2036 1484- gag/pol/vif/vpr/tat/rev/vpu/env 102 2308, 5041- 6251 hiv47 NL43_A00B05C01D00E00F00G00 1812 1484- gag/pol 103 2308, 3620- 4606 hiv48 NL43_A00B05C01D01E00F00G00 2798 1484- gag/pol/vif/vpr/tat/rev 104 2308, 3620- 4606, 5073- 6058 hiv49 NL43_A00B05C01D04E00F00G00 3023 1484- gag/pol/vif/vpr/tat/rev/vpu/env 105 2308, 3620- 4606, 5041- 6251 hiv50 NL43_A00B06C00D01E00F00G00 1846 1469- gag/pol/vif/vpr/tat/rev 106 2328, 5073- 6058 hiv51 NL43_A00B06C00D04E00F00G00 2071 1469- gag/pol/vif/vpr/tat/rev/vpu/env 107 2328, 5041- 6251 hiv52 NL43_A00B06C01D00E00F00G00 1847 1469- gag/pol 108 2328, 3620- 4606 hiv53 NL43_A00B06C01D01E00F00G00 2833 1469- gag/pol/vif/vpr/tat/rev 109 2328, 3620- 4606, 5073- 6058 hiv54 NL43_A00B06C01D04E00F00G00 3058 1469- gag/pol/vif/vpr/tat/rev/vpu/env 110 2328, 3620- 4606, 5041- 6251 hiv55 NL43_A00B07C00D00E00F00G00 796 1560- gag/pol 111 2355 hiv56 NL43_A00B07C00D01E00F00G00 1782 1560- gag/pol/vif/vpr/tat/rev 112 2355, 5073- 6058 hiv57 NL43_A00B07C00D04E00F00G00 2007 1560- gag/pol/vif/vpr/tat/rev/vpu/env 113 2355, 5041- 6251 hiv58 NL43_A00B07C01D00E00F00G00 1783 1560- gag/pol 114 2355, 3620- 4606 hiv59 NL43_A00B07C01D01E00F00G00 2769 1560- gag/pol/vif/vpr/tat/rev 115 2355, 3620- 4606, 5073- 6058 hiv60 NL43_A00B07C01D04E00F00G00 2994 1560- gag/pol/vif/vpr/tat/rev/vpu/env 116 2355, 3620- 4606, 5041- 6251

TABLE 5 total bases deletion genes/regions partially or strain plasmid_name seq name deleted interval(s) fully deleted BTN400 pUC19- hiv20 NL43_A00B01C 1016 1636-2651 gag/pol NL43_A00B01C00 00D00E00F00G D00E00F00G00 00 BTN401 pUC19- hiv21 NL43_A00B01C 2002 1636-2651, gag/pol/vif/vpr/tat/rev NL43_A00B01C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN402 pUC19- hiv22 NL43_A00B01C 2227 1636-2651, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B01C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN403 pUC19- hiv24 NL43_A00B01C 2989 1636-2651, gag/pol/vif/vpr/tat/rev NL43_A00B01C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN404 pUC19- hiv26 NL43_A00B02C 1361 1455-2815 gag/pol NL43_A00B02C00 00D00E00F00G D00E00F00G00 00 BTN405 pUC19- hiv27 NL43_A00B02C 2347 1455-2815, gag/pol/vif/vpr/tat/rev NL43_A00B02C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN406 pUC19- hiv28 NL43_A00B02C 2572 1455-2815, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B02C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN407 pUC19- hiv29 NL43_A00B02C 2348 1455-2815, gag/pol NL43_A00B02C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN408 pUC19- hiv30 NL43_A00B02C 3334 1455-2815, gag/pol/vif/vpr/tat/rev NL43_A00B02C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN409 pUC19- hiv31 NL43_A00B02C 3559 1455-2815, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B02C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN410 pUC19- hiv33 NL43_A00B03C 2533 1448-2994, gag/pol/vif/vpr/tat/rev NL43_A00B03C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN411 pUC19- hiv34 NL43_A00B03C 2758 1448-2994, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B03C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN412 pUC19- hiv38 NL43_A00B04C 908 1469-2376 gag/pol NL43_A00B04C00 00D00E00F00G D00E00F00G00 00 BTN413 pUC19- hiv39 NL43_A00B04C 1894 1469-2376, gag/pol/vif/vpr/tat/rev NL43_A00B04C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN414 pUC19- hiv40 NL43_A00B04C 2119 1469-2376, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B04C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN415 pUC19- hiv41 NL43_A00B04C 1895 1469-2376, gag/pol NL43_A00B04C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN416 pUC19- hiv42 NL43_A00B04C 2881 1469-2376, gag/pol/vif/vpr/tat/rev NL43_A00B04C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN417 pUC19- hiv43 NL43_A00B04C 3106 1469-2376, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B04C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN418 pUC19- hiv44 NL43_A00B05C 825 1484-2308 gag/pol NL43_A00B05C00 00D00E00F00G D00E00F00G00 00 BTN419 pUC19- hiv45 NL43_A00B05C 1811 1484-2308, gag/pol/vif/vpr/tat/rev NL43_A00B05C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN420 pUC19- hiv46 NL43_A00B05C 2036 1484-2308, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B05C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN421 pUC19- hiv47 NL43_A00B05C 1812 1484-2308, gag/pol NL43_A00B05C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN422 pUC19- hiv48 NL43_A00B05C 2798 1484-2308, gag/pol/vif/vpr/tat/rev NL43_A00B05C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN423 pUC19- hiv49 NL43_A00B05C 3023 1484-2308, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B05C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN424 pUC19- hiv50 NL43_A00B06C 1846 1469-2328, gag/pol/vif/vpr/tat/rev NL43_A00B06C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN425 pUC19- hiv51 NL43_A00B06C 2071 1469-2328, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B06C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN426 pUC19- hiv53 NL43_A00B06C 2833 1469-2328, gag/pol/vif/vpr/tat/rev NL43_A00B06C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN427 pUC19- hiv54 NL43_A00B06C 3058 1469-2328, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B06C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN428 pUC19- hiv55 NL43_A00B07C 796 1560-2355 gag/pol NL43_A00B07C00 00D00E00F00G D00E00F00G00 00 BTN429 pUC19- hiv56 NL43_A00B07C 1782 1560-2355, gag/pol/vif/vpr/tat/rev NL43_A00B07C00 00D01E00F00G 5073-6058 D01E00F00G00 00 BTN430 pUC19- hiv57 NL43_A00B07C 2007 1560-2355, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B07C00 00D04E00F00G 5041-6251 D04E00F00G00 00 BTN431 pUC19- hiv58 NL43_A00B07C 1783 1560-2355, gag/pol NL43_A00B07C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN432 pUC19- hiv59 NL43_A00B07C 2769 1560-2355, gag/pol/vif/vpr/tat/rev NL43_A00B07C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN433 pUC19- hiv60 NL43_A00B07C 2994 1560-2355, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B07C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN434 pUC19- hiv23 NL43_A00B01C 2003 1636-2651, gag/pol NL43_A001301C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN435 pUC19- hiv23 NL43_A00B01C 2003 1636-2651, gag/pol NL43_A001301C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN436 pUC19- hiv25 NL43_A00B01C 3214 1636-2651, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B01C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN437 pUC19- hiv25 NL43_A00B01C 3214 1636-2651, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B01C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN438 pUC19- hiv32 NL43_A00B03C 1547 1448-2994 gag/pol NL43_A00B03C00 00D00E00F00G D00E00F00G00 00 BTN439 pUC19- hiv32 NL43_A00B03C 1547 1448-2994 gag/pol NL43_A00B03C00 00D00E00F00G D00E00F00G00 00 BTN440 pUC19- hiv35 NL43_A00B03C 2534 1448-2994, gag/pol NL43_A00B03C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN441 pUC19- hiv35 NL43_A00B03C 2534 1448-2994, gag/pol NL43_A00B03C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN442 pUC19- hiv36 NL43_A00B03C 3520 1448-2994, gag/pol/vif/vpr/tat/rev NL43_A00B03C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN443 pUC19- hiv36 NL43_A00B03C 3520 1448-2994, gag/pol/vif/vpr/tat/rev NL43_A00B03C01 01D01E00F00G 3620-4606, D01E00F00G00 00 5073-6058 BTN444 pUC19- hiv37 NL43_A00B03C 3745 1448-2994, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B03C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN445 pUC19- hiv37 NL43_A00B03C 3745 1448-2994, gag/pol/vif/vpr/tat/rev/vpu/env NL43_A00B03C01 01D04E00F00G 3620-4606, D04E00F00G00 00 5041-6251 BTN446 pUC19- hiv52 NL43_A00B06C 1847 1469-2328, gag/pol NL43_A00B06C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN447 pUC19- hiv52 NL43_A00B06C 1847 1469-2328, gag/pol NL43_A00B06C01 01D00E00F00G 3620-4606 D00E00F00G00 00 BTN454 pUC19- hiv20 NL43_A00B01C 1016 1636-2651 gag/pol NL43_A00B01C00 00D00E00F00G D00E00F00G00 00 BTN477 pUC19- hiv02 NL43_A00B00C 986 5073-6058 vif/vpr/tat/rev NL43_A00B00C00 00D01E00F00G D01E00F00G00 00 BTN478 pUC19- hiv04 NL43_A00B00C 986 5073-6058 vif/vpr/tat/rev NL43_A00B00C00 00D0E00F00G D02E00F00G00 00 BTN479 pUC19- hiv06 NL43_A00B00C 1089 5071-6159 vif/vpr/tat/rev/vpu NL43_A00B00C00 00D03E00F00G D03E00F00G00 00 BTN480 pUC19- hiv08 NL43_A00B00C 1211 5041-6251 vif/vpr/tat/rev/vpu/env NL43_A00B00C00 00D04E00F00G D04E00F00G00 00 BTN481 pUC19- hiv03 NL43_A00B00C 1160 5073-6058, vif/vpr/tat/rev/nef/U3 NL43_A00B00C00 00D01E00F01G 9116-9289 D01E00F01G00 00 BTN482 pUC19- hiv05 NL43_A00B00C 1160 5073-6058, vif/vpr/tat/rev/nef/U3 NL43_A00B00C00 00D02E00F01G 9116-9289 D02E00F01G00 00 BTN483 pUC19- hiv07 NL43_A00B00C 1263 5071-6159, vif/vpr/tat/rev/vpu/nef/U3 NL43_A00B00C00 00D03E00F01G 9116-9289 D03E00F01G00 00 BTN484 pUC19- hiv09 NL43_A00B00C 1385 5041-6251, vif/vpr/tat/rev/vpu/env/nef/U3 NL43_A00B00C00 00D04E00F01G 9116-9289 D04E00F01G00 00 BTN485 pUC19- hiv09 NL43_A00B00C 1385 5041-6251, vif/vpr/tat/rev/vpu/env/nef/U3 NL43_A00B00C00 00D04E00F01G 9116-9289 D04E00F01G00 00 BTN486 pUC19- hiv09 NL43_A00B00C 1385 5041-6251, vif/vpr/tat/rev/vpu/env/nef/U3 NL43_A00B00C00 00D04E00F01G 9116-9289 D04E00F01G00 00 BTN487 pUC19- hiv10 NL43_A00B00C 987 3620-4606 pol NL43_A00B00C01 01D00E00F00G D00E00F00G00 00 BTN488 pUC19- hiv10 NL43_A00B00C 987 3620-4606 pol NL43_A00B00C01 01D00E00F00G D00E00F00G00 00 BTN489 pUC19- hiv12 NL43_A00B00C 1973 3620-4606, pol/vif/vpr/tat/rev NL43_A00B00C01 01D01E00F00G 5073-6058 D01E00F00G00 00 BTN490 pUC19- hiv14 NL43_A00B00C 1973 3620-4606, pol/vif/vpr/tat/rev NL43_A00B00C01 01D02E00F00G 5073-6058 D02E00F00G00 00 BTN491 pUC19- hiv14 NL43_A00B00C 1973 3620-4606, pol/vif/vpr/tat/rev NL43_A00B00C01 01D02E00F00G 5073-6058 D02E00F00G00 00 BTN492 pUC19- hiv16 NL43_A00B00C 2076 3620-4606, pol/vif/vpr/tat/rev/vpu NL43_A00B00C01 01D03E00F00G 5071-6159 D03E00F00G00 00 BTN493 pUC19- hiv16 NL43_A00B00C 2076 3620-4606, pol/vif/vpr/tat/rev/vpu NL43_A00B00C01 01D03E00F00G 5071-6159 D03E00F00G00 00 BTN494 pUC19- hiv18 NL43_A00B00C 2198 3620-4606, pol/vif/vpr/tat/rev/vpu/env NL43_A00B00C01 01D04E00F00G 5041-6251 D04E00F00G00 00 BTN495 pUC19- hiv18 NL43_A00B00C 2198 3620-4606, pol/vif/vpr/tat/rev/vpu/env NL43_A00B00C01 01D04E00F00G 5041-6251 D04E00F00G00 00 BTN496 pUC19- hiv11 NL43_A00B00C 1161 3620-4606, pol/nef/U3 NL43_A00B00C01 01D00E00F01G 9116-9289 D00E00F01G00 00 BTN497 pUC19- hiv13 NL43_A00B00C 2147 3620-4606, pol/vif/vpr/tat/rev/nef/U3 NL43_A00B00C01 01D01E00F01G 5073-6058, D01E00F01G00 00 9116-9289 BTN498 pUC19- hiv15 NL43_A00B00C 2147 3620-4606, pol/vif/vpr/tat/rev/nef/U3 NL43_A00B00C01 01D02E00F01G 5073-6058, D02E00F01G00 00 9116-9289 BTN499 pUC19- hiv17 NL43_A00B00C 2250 3620-4606, pol/vif/vpr/tat/rev/vpu/nef/U3 NL43_A00B00C01 01D03E00F01G 5071-6159, D03E00F01G00 00 9116-9289 BTN500 pUC19- hiv17 NL43_A00B00C 2250 3620-4606, pol/vif/vpr/tat/rev/vpu/nef/U3 NL43_A00B00C01 01D03E00F01G 5071-6159, D03E00F01G00 00 9116-9289 BTN501 pUC19- hiv19 NL43_A00B00C 2372 3620-4606, pol/vif/vpritat/rev/vpu/envinef/U3 NL43_A00B00C01 01D04E00F01G 5041-6251, D04E00F01G00 00 9116-9289 BTN502 pUC19- hiv19 NL43_A00B00C 2372 3620-4606, pol/vif/vpr/tat/rev/vpu/env/nef/U3 NL43_A00B00C01 01D04E00F01G 5041-6251, D04E00F01G00 00 9116-9289 BTN503 pUC19- hiv00 NL43_A00B00C 0 none none NL43_A00B00C00 00D00E00F00G D00E00F00G00 00 BTN504 pUC19- hiv01 NL43_A00B00C 174 9116-9289 nef/U3 NL43_A00B00C00 00D00E00F01G D00E00F01G00 00

Construction of Wildtype Single-Block Plasids

All preparative PCR was performed using Q5 Hot Start High-Fidelity DNA Polymerase (New England Biolabs, #M0493L), hereafter referred to as Q5. All PCR was conducted at the 50 μl scale in 1x Q5 Reaction Buffer supplemented with single-thaw aliquots of dNTPs and with thermocycler parameters recommended by the Q5 manufacturer's protocol. Oligonucleotide sequences are listed in Table 6.

TABLE 6 SEQ ID num name sequence NO. y530 oTN5-F /5Phos/CTGTCTCTTATACACATCTGCGGCCGC 117 y531 oTN5-R /5Phos/CTGTCTCTTATACACATCTTTAATTAATTCGCTACC 118 y468 oBC20v1-F CCGTCCATGAAGGGTTCGAT 119 y469 oBC20v1-R ACGAATCTGCCGTTGCCATA 120 y456 oBC20v1-T CCGTCCATGAAGGGTTCGATNNNNNNNNNNNNNNNNNNNNT 121 ATGGCAACGGCAGATTCGT y541 opUC19_ TCTAGAGTCGACCTGCAGGCATGC 122 BamHI-F y542 opUC19_ CCGGGTACCGAGCTCGAATTCACT 123 BamHI-R y126 oNL43pol-F GAGACAGGGCAAGAAACAGC 124 y127 oNL43pol-R AACAGGCGGCCTTAACTGTA 125 y229 oMS2-F TCCTGCTCAACTTCCTGTCGAG 126 y230 oMS2-R CAGGTCAAACCTCCTAGGAATG 127 y470 opUC19Δ1-F AGTGTAAAGCCTGGGGTGCCT 128 y471 opUC19Δ1-R TGACTGGGAAAACCCTGGCGT 129 y472 opUC19Δ2-F ATTGCGTTGCGCTCACTGCC 130 y473 opUC19Δ2-R GCCCTTCCCAACAGTTGCG 131 y474 oNL43_A0_ TTGTAAAACGACGGCCAGTGAATTCGAGCTCGGTACCCGGAG 132 inner-F GCCTCCACCTGGGTCTTG y475 oNL43_A0_ GCGGCCGCAGGCGATTAAGTTGGGTAACGCCAGGGTTTTCC 133 outer-F CAGTCACGGCGCGCCTTGTAAAACGACGGCCAGTGAATTC y476 oNL43_A0-R GCGGCCGCAGGCCCTGCATGCACTGGATGCAATCTATCCCAT 134 TCTGCA y477 oNL43_B0-F GCGGCCGCTGCAGAATGGGATAGATTGCATCCAGTGCATGCA 135 GGGCCT y478 oNL43_B0-R GCGGCCGCAGCTGTCCTTTTCTGGCAGCACTATAGGCTGTAC 136 TGTCCA y479 oNL43_C0-F GCGGCCGCTGGACAGTACAGCCTATAGTGCTGCCAGAAAAG 137 GACAGCT y480 oNL43_C0_ CATTAGGCACCCCAGGCTTTACACTGGCGCGCCATCTTGTAT 138 inner-R TACTACTGCCCCTTCACCTTTCCAGAGGAGC y481 oNL43_C0_ GCGGCCGCGTGAGTTAGCTCACTCATTAGGCACCCCAGGCTT 139 outer-R TACACT y482 oNL43_D0-F AGGCGATTAAGTTGGGTAACGCCAGGGTTTTCCCAGTCACGG 140 CGCGCCGCTCCTCTGGAAAGGTGAAGGGGCAGTAGTAATAC AAGAT y483 oNL43_D0-R GTGAGTTAGCTCACTCATTAGGCACCCCAGGCTTTACACTGG 141 CGCGCCCATTTACCAATACTACTTCTTGTGGGTTGGGGTCTGT GGG y484 oNL43_E0_ GTAACGCCAGGGTTTTCCCAGTCACGGCGCGCCCCCACAGA 142 inner-F CCCCAACCCACAAGAAGTAGTATTGGTAAATG y485 oNL43_E0_ GCGGCCGCAGGCGATTAAGTTGGGTAACGCCAGGGTTTTCC 143 outer-F CAGTCAC y486 oNL43_E0-R GCGGCCGCGCACAGGCTCCGCAGATCGTCCCAGATAAGTGC 144 TAAGGAT y487 oNL43_F0-F GCGGCCGCATCCTTAGCACTTATCTGGGACGATCTGCGGAGC 145 CTGTGC y488 oNL43_F0-R GCGGCCGCGCAGCTCTCGGGCCACGTGATGAAATGCTAGGC 146 GGCTGTC y489 oNL43_G0-F GCGGCCGCGACAGCCGCCTAGCATTTCATCACGTGGCCCGA 147 GAGCTGC y490 oNL43_G0_ TGATTACGCCAAGCTTGCATGCCTGCAGGTCGACTCTAGAGC 148 inner-R GCGATCTTGGCTCACTGC y491 oNL43_G0_ GCGGCCGCGTGAGTTAGCTCACTCATTAGGCACCCCAGGCTT 149 outer-R TACACTGGCGCGCCTGATTACGCCAAGCTTGCATGCCTG y661 oNL43_AB-F GCATCCAGTGCATGCAGGGCCT 150 y662 oNL43_BC-R CTGGCAGCACTATAGGCTGTACTGTCCA 151 y663 oNL43_BC-F TGGACAGTACAGCCTATAGTGCTGCCAG 152 y664 oNL43_CD-R CTACTGCCCCTTCACCTTTCCAGAGGAGC 153 y665 oNL43_CD-F GCTCCTCTGGAAAGGTGAAGGGGCAGTAG 154 y666 oNL43_DE-R CTACTTCTTGTGGGTTGGGGTCTGTGGG 155 y667 oNL43_DE-F CCCACAGACCCCAACCCACAAGAAGTAG 156 y668 oNL43_EF-R GGCTCCGCAGATCGTCCCAGATAAGTGC 157 y669 oNL43_EF-F GCACTTATCTGGGACGATCTGCGGAGCC 158 y670 oNL43_FG-R GGCCACGTGATGAAATGCTAGGCGGC 159 y671 oNL43_FG-F GCCGCCTAGCATTTCATCACGTGGCC 160 y672 oNL43_gag TGGGACAGCTACAACCATCCCT 161 MA_178 bp-F y673 oNL43_gag GCTGCTGCTTGCTGTGCCTT 162 MA_178 bp-R

Linearized vectors were prepared by 15 cycles of PCR using 1 ng of pUC19 as template with Q5. pUC19Δ1 was obtained by PCR with oligos y470 and y471. pUC19Δ2 was obtained by PCR with oligos y472 and y473 that had been 5′ phosphorylated with T4 PNK (New England Biolabs). pUC19Bam was obtained by PCR with oligos y541 and y542. After the cycling was completed, each reaction was supplemented with 20 U of Dpnl (New England Biolabs), mixed, then incubated for 1 h at 37° C. to eliminate template DNA, then purified by a silica column cleanup with Zymo DCC-5 (Zymo Research, DCC-5). The NL43-WT cloning PCR scheme is provided below in Table 7.

TABLE 7 NL43-WT-cloning-PCR-scheme name size template fwd olig. rev olig. pUC19Δ1 2522 pUC19/BamHI y470 y471 pUC19Δ2 2384 pUC19/BamHI y472 + P_(i) y473 + P_(i) pUC19Bam 2684 pUC19/BamHI y541 y542 NL43_A00_inner 1788 pNL4-3/EcoRI y474 y476 + P_(i) NL43_A00 1844 NL43_A00_inner y475 + P_(i) y476 + P_(i) NL43_B00 1904 pNL4-3/EcoRI y477 + P_(i) y478 + P_(i) NL43_C00_inner 1766 pNL4-3/EcoRI y479 + P_(i) y480 NL43_C00 1789 NL43_C00_inner y479 + P_(i) y481 + P_(i) NL43_D00 1633 pNL4-3/EcoRI y482 + P_(i) y483 + P_(i) NL43_E00_inner 2102 pNL4-3/BamHI y484 y486 + P_(i) NL43_E00 2125 NL43_E00_inner y485 + P_(i) y486 + P_(i) NL43_F00 931 pNL4-3/EcoRI y487 + P_(i) y488 + P_(i) NL43_G00_inner 453 pNL4-3/BamHI y489 + P_(i) y490 NL43_G00 509 NL43_G00_inner y489 + P_(i) y491 + P_(i)

Three of the seven single-block inserts (NL43_B00, NL43_D00 and NL43_F00) were amplified by 15 cycles of PCR using 1 ng of BamHI- or EcoRI-cut pNL4-3 as template and the oligos listed in Table 6. Post-thermocycling, each reaction was supplemented with 20 U of Dpnl (New England Biolabs), mixed, then incubated for 1 h at 37° C. to eliminate template DNA, then purified by a silica column cleanup with Zymo DCC-5 (Zymo Research, DCC-5).

The remaining four single-block inserts (NL43_A00, NL43_C00, NL43_E00, NL43_G00) were amplified by two rounds of PCR, using the oligos listed in Table 6. An “inner” PCR product was obtained by 15 cycles of PCR using 1 ng of EcoRl-cut pNL4-3 as template. The final linear product was obtained by an additional 10 cycles of PCR, using 0.5 μl of the “inner” PCR product as template in a new 50 μl PCR reaction. Post-thermocycling, each reaction was supplemented with 20 U of Dpn*I (New England Biolabs), mixed, then incubated for 1 h at 37° C. to eliminate template DNA, then purified by a silica column cleanup with Zymo DCC-5 (Zymo Research, DCC-5).

Single-block plasmids were constructed by TA-cloning. Linearized vectors (pUC19Δ1 and pUC19Δ1) were 3′ dA-tailed by incubating 2 μg linear vector DNA, 200 μM dATP, 15 U of Klenow Fragment (exo⁻) (New England Biolabs), in a 50 μl reaction in 1x NEB Buffer 2 for 2 h at 37° C. DNA was purified from the reaction by DCC-5 silica column cleanup (Zymo Research). The seven wildtype inserts (NL43_A00, NL43_B00, . . . , NL43_G00) were 3′ dT-tailed by incubating 2 μg insert DNA, 200 μM dTTP, 15 U of Klenow Fragment (exo⁻) (New England Biolabs), in a 50 μl reaction in 1x NEB Buffer 2 for 2 hours at 37° C. DNA was purified from the reaction by DCC-5 silica column cleanup (Zymo Research).

All ligations were performed using T4 DNA Ligase (New England Biolabs, Quick Ligation Kit, #M2200L). To construct pUC19Δ1-NL43_D00, 50 ng of 3′ dT-tailed NL43_D00 were ligated into 50 ng of 3′ dA-tailed pUC19A1 in a 20 μl reaction for 30 min at 25° C.

To construct the remaining six single-block wildtype plasmids (-NL43_x, where x is one of {A00,B00,C00,E00,F00,G00}), 50 ng of 3′ dT-tailed NL43_x were ligated into 50 ng of 3′ dA-tailed in a 20 μl reaction for 30 min at 25° C.

Chemically competent DH10B E. coli were transformed with the ligation mixture, recovered for 1 hour at 37° C., then plated on LB plates supplemented with 100 μg/ml carbenicillin and grown overnight at 37° C. Single colonies were obtained and plasmids characterized by Sanger sequencing across the insert region and diagnostic restriction digests. All wildtype single-block plasmids are enumerated in Table 3.

Construction of Mutant Single-Block Plasmids

Deletion mutant pieces were ordered as synthetic dsDNA molecules (Integrated DNA Technologies, gBlocks). A total of 13 mutant blocks were ordered (7× B-blocks (B01, B02, B03, B04, B05, B06, B07), 1×C-block (001), 4×D-blocks (D01, D02, D03, D04), and 1×F-block (F01)).

Mutant blocks NL43_D01, NL43_D02, NL43_D03, and NL43 DO4 were cloned into pUC19Δ1 linear PCR product by Gibson Assembly (Gibson Assembly HiFi 1-Step Kit, SGI-DNA) via the manufacturer's protocol. The remaining 9 mutant blocks (NL43_B01, . . . ,NL43_F01) were cloned into pUC19,82 linear PCR product by Gibson Assembly (Gibson Assembly HiFi 1-Step Kit, SGI-DNA). After a 1 hour incubation at 50° C., the 10 μl Gibson Assembly reactions were diluted by adding 50 μl of TE. One μl of the diluted mix was used to transform 40 μl of electrocompetent DH10B E. coli. The transformations were recovered for 1 hour at 37° C., then plated on LB plates supplemented with 100 μg/ml carbenicillin and grown overnight at 37° C. Single colonies were obtained and plasmids characterized by Sanger sequencing across the insert region and diagnostic restriction digests. All single-block plasmids are enumerated in Table 8.

TABLE 8 NL4-3-singlePiecePlasmids name size insert backbone enzyme pUC19Δ2-NL43_A00 4229 1836 2394 Notl pUC19Δ2-NL43_B00 4290 1896 2394 Notl pUC19Δ2-NL43_B01 3334 935 2394 Notl pUC19Δ2-NL43_B02 2989 590 2394 Notl pUC19Δ2-NL43_B03 2803 404 2394 Notl pUC19Δ2-NL43_B04 3442 1043 2394 Notl pUC19Δ2-NL43_B05 3525 1126 2394 Notl pUC19Δ2-NL43_B06 3490 1091 2394 Notl pUC19Δ2-NL43_B07 3554 1155 2394 Notl pUC19Δ2-NL43_C00 4174 1781 2394 Notl pUC19Δ2-NL43_C01 3250 857 2394 Notl pUC19Δ1-NL43_D00 4076 1545 2531 Ascl pUC19Δ1-NL43_D01 622 622 2531 Ascl pUC19Δ1-NL43_D02 561 561 2531 Ascl pUC19Δ1-NL43_D03 519 519 2531 Ascl pUC19Δ1-NL43_D04 397 397 2531 Ascl pUC19Δ2-NL43_E00 4510 2117 2394 Notl pUC19Δ2-NL43_F00 3317 923 2394 Notl pUC19Δ2-NL43_F01 3205 812 2394 Notl pUC19Δ2-NL43_G00 2895 501 2394 Notl

Construction of 3-Block Plasmids

To construct plasmids harboring subassemblies of 3 blocks (ABC or EFG as shown in FIG. 39, single blocks were liberated from their respective plasmids by digestion and gel-purified from plasmid backbone. To assemble ABC 3-block plasmids, a pool of liberated A,B,C blocks were combined with linear pUC19Δ1 and incubated for 1 hour at 50° C. in Gibson Assembly master mix (Gibson Assembly HiFi 1-Step Kit, SGI-DNA). To assemble EFG 3-block plasmids, a pool of liberated E,F,G blocks were combined with linear pUC19,82 and incubated for 1 hour at 50° C. in Gibson Assembly master mix (Gibson Assembly HiFi 1-Step Kit, SGI-DNA).

After a 1 hour incubation at 50° C., the 10 μl Gibson Assembly reactions were diluted by adding 50 μl of TE. One μl of the diluted mix used to transform 40 μl of electrocompetent DH1OB E. coli.

The transformations were recovered for 1 hour at 37° C., then plated on LB plates supplemented with 100 μg/ml carbenicillin and grown overnight at 37° C. Single colonies were obtained and plasmids characterized by Sanger sequencing across junction regions joined by Gibson Assembly and diagnostic restriction digests.

Construction of 7-Block Plasmids (Full-Length Virus)

3-block inserts (ABC and EFG) were liberated from 3-block plasmids by digestion with Ascl and gel-purified from the backbone. D blocks were liberated by digestion of 1-block D plasmids. A three-insert Gibson assembly was performed by combining an ABC 3-block insert, a D-block insert, and a EFG 3-block insert with pUC19Bam and incubated 1 hour at 50° C. in Gibson Assembly master mix (Gibson Assembly HiFi 1-Step Kit, SGI-DNA) per the manufacturer's instruction.

After a 1 hour incubation at 50° C., the 10 μl Gibson Assembly reactions were diluted by adding 50 μl of TE. One μl of the 1:5 diluted mix used to transform 40 μl of electrocompetent DH1OB E. coli.

The transformations were recovered for 90 min at 30° C., then plated on LB plates supplemented with 25 μg/ml carbenicillin and grown overnight at 32° C. Single colonies were obtained and plasmids characterized by Sanger sequencing across junction regions joined by Gibson Assembly. Diagnostic restriction digests were also performed to confirm that the 7-block plasmids had the correct topology. All 7-block plasmids (full-length virus) are listed in Table 5.

Characterization of Deletion Mutants

Deletion mutants were assayed for three properties: replication-competence (can spread without wildtype virus), interfere with WT virus (by competing for common goods or another mechanism), and mobilized by the wildtype virus (efficiently trans-complemented. Supercoiled plasmid stocks of the mutant library were arrayed in 96-well plate format at a normalized DNA concentration (33 ng/). The collection of deletion mutants used the same vector backbone as the wildtype HIV-1 and had similar sizes (9-12 kbp mutants compared to 15 kbp wildtype). A related HIV-1 molecular clone (NLENG1-I RES), which we refer to as NL43G was used as positive control. NL43G is tagged with EGFP in the nef locus. Productively infected cells can be visualized by GFP fluorescence after approximately 20 hours of infection.

Production of Virus and Pseudovirus Stocks

Virus pools were obtained by co-transfection of 293T with one or more plasmids. On the day of transfection, a suspension of 293T was obtained by trypsinization of subconfluent 15-cm plates of 293T and brought into single cell suspension by gentle passage through a 40 μm mesh filter (Corning). A cell count was obtained with an automated Coulter cell counter (Moxi, ORFLO), and cells were diluted to a concentration of 5·10⁵ cells/ml in D10. Two ml of this suspension (10⁶ cells) were added to each well of a series of 6-well polystyrene tissue culture plates.

Transfection complexes were prepared in 96-well polypropylene PCR plates under sterile conditions. A total of 2 μg of supercoiled plasmid DNA in (10 mM Tris-Cl, pH 8.0; 0.1 mM EDTA, pH 8.0) was added to each well and the volume brought to 100 μl by the addition of serum-free DMEM supplemented with 25 mM HEPES. Next, 106 μg of a mixture comprised of 100:6 (v:v) of serum free-DMEM supplemented with 25 mM HEPES and 1 mg/ml polyethyleneimine (PEI) in dH₂O (prepared from 25 kDa linear PEI; Polysciences #23966-1) were added and the contents mixed by pipetting up and down 15× with the multichannel pipette volume set to 106 μl. The transfection mixture was incubated at room temperature (24° C.) for 15 min, then the contents of each well in the 96-well plate added to a corresponding well of 10⁶ 293T prepared above. The 6-well plates were gently rocked to distribute the transfection complexes, and then placed in a humidified 37° C. incubator with a 95% air/5% CO₂ atmosphere. At 16 h post-transfection, the culture media was aspirated and replaced with 2.5 ml of D10. At 43-48 hours post-transfection, the virus-containing media was harvested and clarified by passage through a 0.45 μm sterile filter (Millipore). The filtrate was immediately used to infect target cells.

Determination of Replication Competence

Virus stocks were prepared as described above, where the 2 μg mass of plasmid DNA in each well was comprised entirely of a single HIV-1 molecular clone or deletion mutant. An EGFP-tagged molecular clone (pNLENG1-IRES), which encodes NL4-3 with an EGFP::IRES::nef cassette in the nef locus was used as a positive control for replication competence (Levy, D. N. et al. PNAS, 101, 4204-4209 (2004)). We refer to this clone as NL43G for simplicity.

MT-4 (Miyoshi, I. et al. Gann. Monogr., 28 (1982)), (a highly-permissive, highly-susceptible T cell line) were infected with the prepared viral stocks in a 96-well U-bottom plate format. All infections were performed in duplicate. In each well, 10⁵ MT-4 in 150 μl of R10 were mixed with 50 μl of virus stock by pipetting up and down 4x, and then returned to a 37° C. incubator. Cultures were split 1:10 with fresh media every 3-4 days and the wells assayed for infection visually (for cytopathic effect/cell lysis) at each split.

At 5 days post-infection, 90 μl of the cell mixture from each well were transferred to a 96-well opaque plastic plate (OptiPlate96-F, PerkinElmer) and mixed with 10 μl of PrestoBlue Cell Viability Reagent (ThermoFisher, #A13261). The plate was sealed with a gas-permeable adhesive seal (ThermoFisher, #AB0718) and incubated for 90 min at 37° C. The reaction was quenched and virus inactivated by addition of 50 μl of 3% (m/v) SDS solution to each well. Fluorescence was read on an EnSpire Plate Reader (PerkinElmer) with the monochromator set to excitation/emission wavelengths of 560/590 nm.

At 5 days post-infection, the MT-4 were assessed for viability visually and by a metabolic assay (PrestoBlue), which detects live, metabolically active cells that have a functional electron transport chain. Thus, wells infected with replication-competent virus will be mostly killed (based on live cell data), and have a low metabolic activity, which is detectable by low fluorescence signal in the plate reader assay.

Interference Assay by Co-Transfection

Virus stocks were prepared as described above, but the 2 μg mass of plasmid DNA in each well was comprised of 1 μg of a single HIV-1 molecular clone or deletion mutant and 1 μg of pNLENG1-IRES.

MT-4 cells were infected with the prepared viral stocks in a 96-well U-bottom plate format. All infections were performed in duplicate. In each well, 10⁵ MT-4 in 150 μl of R10 were mixed with 50 μl of virus stock by pipetting up and down 4×, and then returned to a 37° C. incubator.

At 24 and 48 hours post-infection, cells were resuspended and 50 μl (25% of the volume) removed for analysis by flow cytometry. The 50 μl sample was fixed by addition of 0.1 volumes of a 20% formaldehyde solution (tousimis, #1008A) and incubated for at least 1 hour at 4° C. before cytometry. Cells were scored for EGFP-expression by analyzing a portion of each sample on an HTFC IntelliCyt flow cytometer (488 nm excitation, 530/30 nm bandpass emission).

The cell population was scored for GFP+ cells by flow cytometry at 24 and 48 hpi. All mutants are untagged: the only source of GFP production is infection with wildtype NL43G virus. If a mutant does not interfere with WT virus replication, than the presence or absence of the subgenomic mutant will not affect GFP+levels. Conversely, if we observe a change in GFP+ compared to wildtype (NL43G only), the mutant either enhances wildtype virus replication (higher levels of GFP+ cells) or interferes (decreases levels of GFP+cells).

Assay for Mobilization from 293T

Cloned mutants were tested for transmissibility: could they be encapsidated and transmitted by supply the missing trans-acting elements via transfection. A packaging cell line (239T) was co-transfected with the mutant viral genome plasmid and two additional plasmids: a packaging plasmid (pCMVRΔ8.91), which provides several HIV-1 proteins in trans (Gag, Pol, Tat, Rev), but is not replication-competent), and an envelope pseudotyping plasmid which provides a pan-tropic VSV-G envelope protein (pMD.G).

Virus stocks were prepared as described above, but the 2 μg mass of plasmid DNA in each well was comprised of 500 ng of a single HIV-1 molecular clone or deletion mutant, 500 ng of a VSV-G pseudotyping plasmid (pMD.G from Naldini, L. Science 272, 263-7 (1996)), and 1000 ng of a 2nd generation lentivirus packaging plasmid (pCMVRΔ8.91 from Zufferey, R. et al. Nature Biotechnology, 15, 871-5, (1997)). 48 hours post-transfection of 293T, virus-containing supernatant was harvested, clarified, and used to transduce a T-cell line (MT-4), and the cells allowed to recover and outgrow for 5 days.

MT-4 cells were transduced/infected with the prepared viral stocks in a 96-well U-bottom plate format. All infections were performed in duplicate. In each well, 10⁵ MT-4 in 150 μl were mixed with 50 μl of virus stock by pipetting up and down 4×, and then returned to a 37° C. incubator. Cultures were split 1:10 with fresh R10 media every 3-4 days and the wells assayed for infection visually (for cytopathic effect/cell lysis) at each split.

At 5 days post-infection, the transduced cells were washed 2× in 700 μl DPBS and genomic DNA isolated from the cell pellet using a commercial kit (Macherey-Nagel, NucleoSpin Blood). Each transduced culture was assessed for transduction efficiency by performing PCR with primers specific to block B and block D, using DNA isolated from the transduced cells as template.

PCR of gDNA isolated from transduced MT-4 was performed to test for transduction/mobilization of DIP candidates. Block B was amplified by PCR from gDNA template with oligos oNL43_AB-F and oNL43_BC-R. Block D was amplified by PCR from gDNA template with oligos oNL43_CD-F and oNL43_DE-R. PCR reactions were performed with OneTaq DNA Polymerase (New England Biolabs, #M0480L). Each 20 μl PCR reaction consisted of 2.0 μl template DNA, 0.4 μl of 10 μM forward oligo, 0.4 μl of 10 μM reverse oligo, 0.4 μl of 10 mM dNTP, 4.0 μl of 5× OneTaq DNA Polymerase Reaction Buffer, 0.1 μl OneTaq DNA Polymerase (5 U/μl), and 12.7 μl dH2O. Thermocycling conditions (in mm:ss format) were (1 cycle of 95° C. for 5:00; 35 cycles of 94° C. for 0:15, 61° C. for 0:30, 68° C. for 1:30; 1 cycle of 68° C. for 5:00; 1 cycle of 10° C. for HOLD).

Results Determination of Replication Competence

As shown in FIG. 42 and FIG. 43, the only clones for which cell killing is evident are NL43G (WT control), the A00B000C00D00E00F00G00 mutant (WT genotype) and a mutant with a single deletion in nef-deletion mutant (F01). This is consistent with literature reports, as nef is dispensable for replication of certain strains of HIV-1 in permissive cells lines, such as MT-4. Thus, this validates that the cloning strategy employed can reconstruct viruses with full wildtype activity.

No loss in cell viability was observed for the other 59 of 61 molecular clones, which contain deletions in one or more essential trans-acting elements. These cultures were outgrown and inspected visually for up to 14 days, but no cytopathic effect of loss of viability was observed in the remaining 59 mutants (data not shown).

Thus, the 59 deletion mutants are not replication-competent and must be trans-complemented by wildtype virus to transmit.

Interference Assay by Co-Transfection

Results of the interference assay are shown in FIG. 44, FIG. 45, FIG. 46, FIG. 47 and FIG. 48.

At 24 hpi (FIG. 44, FIG. 45, FIG. 46), 13-17% of cells were GFP+in the control NL43G infection, compared to <1% in the uninfected control (naive). Co-transfection with the reconstituted replication-competent HIV-1 clones had little effect on single-round wildtype HIV-1 NL43G replication (WT: 11-15% GFP⁺, Δnef. 11-13% GFP⁺).

In contrast, many of the multiply deleted clones showed strong interference with wildtype HIV-1 replication, eliciting 0.5 log₁₀-1.0 log₁₀ reductions in infectious titer with respect to wildtype. The strongest interference effect was observed in clones harboring both deletions in gag and deletions in the accessory tract of the HIV-1 genome (vif-vpu). With no deletions in gag (B00), few of the clones exhibiting strong interference, except for those that also had deletions in pol and nef. No clones showed any consistent enhancement of HIV-1 infection, as defined by an average increase of >30%).

At 24 hpi, the presence (FIG. 46) or absence (FIG. 44 and FIG. 45) of an HIV-1 protease inhibitor (Darunavir) did not affect the percentage of infected cells, reflecting that 24 hpi was appropriate timing to conduct single round studies of HIV-1 replication.

By 48 hpi, (FIG. 47 and FIG. 48), an additional round of HIV-1 replication will have occurred and interference effects will be easily detectable. As before, the strongest interference was observed in clones harboring both deletions in gag and deletions in the accessory tract of the HIV-1 genome (vif-vpu). With no deletions in gag (B00), few of the clones exhibit strong interference, except for those that also had deletions in pol and nef. Again, no clones showed consistent enhancement of HIV-1 infection as defined by an average increase of >30%.

Table 9 (see FIG. 50) serves as map between the data in FIGS. 43, 45, 48 and the sequence associated with each pair of 76 datapoints. In these figures, there are 76 pairs of blue dots moving left to right across the plot, a vertical line, then two pairs of green dots reflecting the controls. Table 9 identifies the mutants that are “replicating” or “not-replicating” (FIG. 43), or “interfering”/“not-interfering” (FIGS. 45 and 48). Some sequences are listed more than once because they had more than one associated bacterial strain (Table 5). The classification is dependent on whether the mean of the pair of points falls within/outside the gray rectangle in the plots.

Table 10 below classifies each of the unique 61 “hiv” sequences as replicating/not-replicating or interfering/not interfering by removing duplicate sequences*.

TABLE 10 FIG. 43 FIG. 45 FIG. 48 does not does not does not replicates replicate interferes interfere interferes interfere 2 of 61 59 of 61 48 of 61 13 of 61 45 of 61 17 of 61 hiv00 hiv09 hiv54 hiv38 hiv54 hiv01 hiv01 hiv19 hiv11 hiv29 hiv58 hiv53 hiv02 hiv58 hiv01 hiv44 hiv19 hiv16 hiv47 hiv26 hiv47 hiv38 hiv52 hiv44 hiv00 hiv55 hiv51 hiv17 hiv60 hiv04 hiv31 hiv29 hiv13 hiv49 hiv05 hiv11 hiv05 hiv14 hiv42 hiv09 hiv60 hiv04 hiv18 hiv55 hiv08 hiv42 hiv26 hiv04 hiv10 hiv06 hiv21 hiv17 hiv11 hiv28 hiv07 hiv28 hiv00 hiv06 hiv31 hiv03 hiv49 hiv09 hiv15 hiv15 hiv02 hiv37 hiv08 hiv08 hiv21 hiv27 hiv06 hiv10 hiv27 hiv23 hiv03 hiv37 hiv14 hiv56 hiv02 hiv20 hiv23 hiv48 hiv07 hiv35 hiv37 hiv24 hiv03 hiv48 hiv32 hiv07 hiv56 hiv45 hiv36 hiv24 hiv14 hiv25 hiv45 hiv10 hiv23 hiv32 hiv30 hiv32 hiv52 hiv15 hiv51 hiv33 hiv36 hiv53 hiv30 hiv52 hiv05 hiv59 hiv25 hiv60 hiv36 hiv59 hiv39 hiv13 hiv33 hiv12 hiv22 hiv46 hiv41 hiv46 hiv35 hiv59 hiv25 hiv22 hiv54 hiv12 hiv13 hiv57 hiv34 hiv43 hiv46 hiv57 hiv50 hiv56 hiv16 hiv40 hiv58 hiv18 hiv34 hiv42 hiv35 hiv12 hiv45 hiv50 hiv57 hiv48 hiv43 hiv39 hiv55 hiv39 hiv18 hiv47 hiv40 hiv16 hiv40 hiv19 hiv41 hiv43 hiv17 hiv20 hiv22 hiv20 hiv19 hiv38 hiv41 hiv30 hiv53 hiv44 hiv51 hiv29 hiv26 hiv50 hiv24 hiv31 hiv27 hiv28 hiv33 hiv49 hiv21 hiv34 *For the hiv19 sequence, one of the “hiv19” clones was classified as “interfering” and the other was classified as “non-interfering”. Assay for Mobilization from 293T

As shown in FIG. 49, the appearance of distinct PCR products at a length less than the WT Block B (1.9 kbp) or WT Block D (1.5 kbp), indicates that MT-4 cells were successfully transduced with the deletion mutant (indicating mobilization) and that the mutant did not lead to cell death (as occurred in some control reactions). For this reason, BTN503 (reconstituted wildtype) and BTN504 (Δnef) showed weak amplification, as the cells were destroyed by viral infection. Approximately 50% (31 of 61) of the deletion mutants showed clear mobilization from 293T from co-transfection. 

1. A method of generating a deletion library, comprising: (a) inserting a transposon cassette comprising a target sequence for a sequence specific DNA endonuclease into a population of circular target DNAs to generate a population of transposon-inserted circular target DNAs; (b) contacting the population of transposon-inserted circular target DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear target DNAs; (c) contacting the population of cleaved linear target DNAs with one or more exonucleases to generate a population of deletion DNAs; and (d) circularizing the deletion DNAs to generate a library of circularized deletion DNAs.
 2. The method of claim 1, wherein the circular target DNAs are plasmids that comprise a viral genome.
 3. The method of claim 2, wherein the method further comprises introducing members of the library of circularized deletion DNAs into mammalian cells, and assaying for viral infectivity.
 4. The method of claim 2, wherein the method further comprises sequencing members of the library of circularized deletion DNAs to identify defective interfering particles (DIPs).
 5. The method of claim 1, wherein the sequence specific DNA endonuclease is selected from: a meganuclease, a CRISPR/Cas endonuclease, a zinc finger nuclease, or a TALEN.
 6. The method of claim 1, wherein the method comprises inserting a barcode sequence prior to or simultaneous with step (d).
 7. The method of claim 1, wherein the one or more exonucleases comprises T4 DNA polymerase.
 8. The method of claim 1, wherein the one or more exonucleases comprises a 3′ to 5′ exonuclease and a 5′ to 3′ exonuclease.
 9. The method of claim 1, wherein the one or more exonucleases comprises RecJ.
 10. The method of claim 1, wherein the step of contacting the population of cleaved linear target DNAs with one or more exonucleases is performed in the presence of a single strand binding protein (SSB).
 11. The method of claim 1, wherein the transposon cassette comprises a first recognition sequence positioned at or near one end of the transposon cassette and a second recognition sequence positioned at or near the other end of the transposon cassette.
 12. The method of claim 1, further comprising, prior to step (a), circularizing a population of linear DNA molecules to generate said population of circular target DNAs.
 13. The method of claim 12, wherein the population of linear DNA molecules comprises one or more PCR products, one or more linear viral genomes, and/or one or more restriction digest products.
 14. The method of claim 1, further comprising introducing members of the library of circularized deletion DNAs into mammalian cells.
 15. The method of claim 1, further comprising generating from the library of circularized deletion DNAs, at least one of: linear double stranded DNA (dsDNA) products, linear single stranded DNA (ssDNA) products, linear single stranded RNA (ssRNA) products, and linear double stranded RNA (dsRNA) products.
 16. The method of claim 15, further comprising introducing said linear dsDNA products, linear ssDNA products, linear ssRNA products, and/or linear dsRNA products into mammalian cells.
 17. A method of generating and identifying a defective interfering particle (DIP), comprising: (a) inserting a target sequence for a sequence specific DNA endonuclease into a population of circular target viral DNAs, each comprising a viral genome, to generate a population of sequence-inserted viral DNAs; (b) contacting the population of sequence-inserted viral DNAs with the sequence specific DNA endonuclease to generate a population of cleaved linear viral DNAs; (c) contacting the population of cleaved linear viral DNAs with an exonuclease to generate a population of deletion DNAs; (d) circularizing the deletion DNAs to generate a library of circularized deletion viral DNAs; and (e) sequencing members of the library of circularized deletion viral DNAs to identify deletion interfering particles (DIPs).
 18. The method of claim 17, comprising, prior to step (a), circularizing a population of linear DNA molecules to generate said population of circular target viral DNAs.
 19. The method of claim 18, wherein the population of linear DNA molecules comprises one or more PCR products, one or more linear viral genomes, and/or one or more restriction digest products.
 20. The method of claim 17, wherein the method comprises inserting a barcode sequence prior to or simultaneous with step (d).
 21. The method of claim 17, further comprising (i) introducing members of the library of circularized deletion viral DNAs into mammalian cells; and (ii) assaying for viral infectivity.
 22. The method of claim 17, further comprising: (i) generating from the library of circularized deletion viral DNAs, at least one of: linear double stranded DNA (dsDNA) products, linear single stranded DNA (ssDNA) products, linear single stranded RNA (ssRNA) products, and linear double stranded RNA (dsRNA) products.
 23. The method of claim 22, further comprising, after step (i): (ii) introducing said linear dsDNA products, linear ssDNA products, linear ssRNA products, and/or linear dsRNA products into mammalian cells; and (iii) assaying for viral infectivity.
 24. The method of claim 12, wherein the inserting of step (a) comprises inserting a transposon cassette into the population of circular target viral DNAs, wherein the transposon cassette comprises the target sequence for the sequence specific DNA endonuclease, and wherein said generated population of sequence-inserted viral DNAs is a population of transposon-inserted viral DNAs.
 25. The method of claim 17, wherein the method comprises, after step (d), infecting mammalian cells in culture with members of the library of circularized deletion viral DNAs at a high multiplicity of infection (MOI), culturing the infected cells for a period of time ranging from 12 hours to 2 days, adding naive cells to the to the culture, and harvesting virus from the cells in culture.
 26. The method of claim 17, wherein the method comprises, after step (d), infecting mammalian cells in culture with members of the library of circularized deletion viral DNAs at a low multiplicity of infection (MOI), culturing the infected cells in the presence of an inhibitor of viral replication for a period of time ranging from 1 day to 6 days, infecting the cultured cells with functional virus at a high MOI, culturing the infected cells for a period of time ranging from 12 hours to 4 days, and harvesting virus from the cultured cells.
 27. A transposon cassette, comprising a DNA molecule comprising transposase compatible inverted terminal repeats (ITRs) flanking a sequence of interest, wherein the sequence of interest comprises a first copy and a second copy of a recognition sequence for a first meganuclease.
 28. The transposon cassette of claim 27, wherein the sequence of interest includes a selectable marker gene, and said first and second copies flank the selectable marker gene.
 29. The transposon cassette of claim 28, wherein the selectable marker gene encodes an antibiotic resistance protein.
 30. The transposon cassette of claim 27, comprising a first copy and a second copy of a recognition sequence for a second meganuclease.
 31. The transposon cassette of claim 30, wherein the first and second copies of the recognition sequence for the second meganuclease flank a selectable marker gene.
 32. The transposon cassette of claim 27, wherein the transposase compatible inverted terminal repeats (ITRs) are cable of being recognized and utilized by a Tn5 transposase. 